Thanks for that, getting a bit further now, but still no luck in compiling. Now I'm getting:

Generating ../build/projects/mess/gmake-mingw64-gcc/yamaha.make...
Generating ../build/projects/mess/gmake-mingw64-gcc/zenith.make...
Generating ../build/projects/mess/gmake-mingw64-gcc/zpa.make...
Generating ../build/projects/mess/gmake-mingw64-gcc/zvt.make...
Generating ../build/projects/mess/gmake-mingw64-gcc/skeleton.make...
Generating ../build/projects/mess/gmake-mingw64-gcc/mess.make...
Done.
Creating ../../../win64_mingw-gcc/bin
Creating ../../../win64_mingw-gcc/bin
Creating ../../../win64_mingw-gcc/bin
Creating ../../../win64_mingw-gcc/bin
Creating ../../../win64_mingw-gcc/bin
Creating ../../../win64_mingw-gcc/bin
Compiling 3rdparty/softfloat/fsincos.c...
Compiling 3rdparty/libjpeg/jaricom.c...
Compiling 3rdparty/zlib/adler32.c...
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-g+
+ -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -I.
./../../../src/emu -I../../../../src/lib -I../../../../src/lib/util -I../../../.
./3rdparty -I../../../../3rdparty/expat/lib -I../../../../src/osd -I../../../../
src/osd/windows -m64 --pipe -Wno-deprecated-declarations -O3 -fno-strict-aliasin
g -Werror -Wno-unknown-pragmas -Wall -Wcast-align -Wundef -Wformat-security -Wwr
ite-strings -Wno-sign-compare -Wno-conversion -Wno-unused-result -Wno-narrowing
-Wno-attributes -Wno-unused-variable -Wno-array-bounds -m64 "-DINLINE=static inl
ine" -x c++ -std=gnu++98 -Woverloaded-virtual -include C:/MAME GitHub/src/osd/wi
ndows/winprefix.h -o ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/softfloat
/fsincos.o -MF ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/softfloat/fsinc
os.d -c ../../../../3rdparty/softfloat/fsincos.c, ...) failed.
Compiling 3rdparty/expat/lib/xmlparse.c...
make (e=2): The system cannot find the file specified.
softfloat.make:259: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/
3rdparty/softfloat/fsincos.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/softfloat/fsinco
s.o] Error 2
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-gc
c -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -m6
4 --pipe -Wno-deprecated-declarations -O3 -fno-strict-aliasing -Werror -Wno-unkn
own-pragmas -Wall -Wcast-align -Wundef -Wformat-security -Wwrite-strings -Wno-si
gn-compare -Wno-conversion -Wno-unused-result -Wno-narrowing -Wno-attributes -Wn
o-unused-variable -Wno-array-bounds -m64 -std=gnu89 -Wpointer-arith -Wbad-functi
on-cast -Wstrict-prototypes -include C:/MAME GitHub/src/osd/windows/winprefix.h
-o ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/libjpeg/jaricom.o -MF ../..
/../win64_mingw-gcc/obj/x64/Release/3rdparty/libjpeg/jaricom.d -c ../../../../3r
dparty/libjpeg/jaricom.c, ...) failed.
make (e=2): The system cannot find the file specified.
jpeg.make:517: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdpa
rty/libjpeg/jaricom.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/libjpeg/jaricom.
o] Error 2
Makefile:22: recipe for target 'softfloat' failed
make[1]: *** [softfloat] Error 2
make[1]: *** Waiting for unfinished jobs....
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-gc
c -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -DZ
LIB_CONST -m64 --pipe -Wno-deprecated-declarations -O3 -fno-strict-aliasing -Wer
ror -Wno-unknown-pragmas -Wall -Wcast-align -Wundef -Wformat-security -Wwrite-st
rings -Wno-sign-compare -Wno-conversion -Wno-unused-result -Wno-narrowing -Wno-a
ttributes -Wno-unused-variable -Wno-array-bounds -m64 -std=gnu89 -Wpointer-arith
-Wbad-function-cast -Wstrict-prototypes -Wno-strict-prototypes -include C:/MAME
GitHub/src/osd/windows/winprefix.h -o ../../../win64_mingw-gcc/obj/x64/Release/
3rdparty/zlib/adler32.o -MF ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/zl
ib/adler32.d -c ../../../../3rdparty/zlib/adler32.c, ...) failed.
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-g+
+ -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -m6
4 --pipe -Wno-deprecated-declarations -O3 -fno-strict-aliasing -Werror -Wno-unkn
own-pragmas -Wall -Wcast-align -Wundef -Wformat-security -Wwrite-strings -Wno-si
gn-compare -Wno-conversion -Wno-unused-result -Wno-narrowing -Wno-attributes -Wn
o-unused-variable -Wno-array-bounds -m64 "-DINLINE=static inline" -x c++ -std=gn
u++98 -Woverloaded-virtual -include C:/MAME GitHub/src/osd/windows/winprefix.h -
o ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/expat/lib/xmlparse.o -MF ../
../../win64_mingw-gcc/obj/x64/Release/3rdparty/expat/lib/xmlparse.d -c ../../../
../3rdparty/expat/lib/xmlparse.c, ...) failed.
make (e=2): The system cannot find the file specified.
Makefile:25: recipe for target 'jpeg' failed
zlib.make:307: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdpa
rty/zlib/adler32.o' failed
make[1]: *** [jpeg] Error 2
make (e=2): The system cannot find the file specified.
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/zlib/adler32.o]
Error 2
expat.make:271: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdp
arty/expat/lib/xmlparse.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/expat/lib/xmlpar
se.o] Error 2
Compiling 3rdparty/libflac/src/libFLAC/bitmath.c...
Makefile:19: recipe for target 'zlib' failed
make[1]: *** [zlib] Error 2
Makefile:16: recipe for target 'expat' failed
make[1]: *** [expat] Error 2
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-gc
c -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -DW
ORDS_BIGENDIAN=0 -DFLAC__NO_ASM -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -DFLA
C__HAS_OGG=0 -DVERSION=\"1.2.1\" -I../../../../3rdparty/libflac/src/libFLAC/incl
ude -I../../../../3rdparty/libflac/include -m64 --pipe -Wno-deprecated-declarati
ons -O3 -fno-strict-aliasing -Werror -Wno-unknown-pragmas -Wall -Wcast-align -Wu
ndef -Wformat-security -Wwrite-strings -Wno-sign-compare -Wno-conversion -Wno-un
used-result -Wno-narrowing -Wno-attributes -Wno-unused-variable -Wno-array-bound
s -m64 -std=gnu89 -Wpointer-arith -Wbad-function-cast -Wstrict-prototypes -Wno-u
nused-function -O0 -include C:/MAME GitHub/src/osd/windows/winprefix.h -o ../../
../win64_mingw-gcc/obj/x64/Release/3rdparty/libflac/src/libFLAC/bitmath.o -MF ..
/../../win64_mingw-gcc/obj/x64/Release/3rdparty/libflac/src/libFLAC/bitmath.d -c
../../../../3rdparty/libflac/src/libFLAC/bitmath.c, ...) failed.
make (e=2): The system cannot find the file specified.
flac.make:331: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdpa
rty/libflac/src/libFLAC/bitmath.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/libflac/src/libF
LAC/bitmath.o] Error 2
make[2]: *** Waiting for unfinished jobs....
Compiling 3rdparty/libflac/src/libFLAC/bitreader.c...
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-gc
c -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -DW
ORDS_BIGENDIAN=0 -DFLAC__NO_ASM -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -DFLA
C__HAS_OGG=0 -DVERSION=\"1.2.1\" -I../../../../3rdparty/libflac/src/libFLAC/incl
ude -I../../../../3rdparty/libflac/include -m64 --pipe -Wno-deprecated-declarati
ons -O3 -fno-strict-aliasing -Werror -Wno-unknown-pragmas -Wall -Wcast-align -Wu
ndef -Wformat-security -Wwrite-strings -Wno-sign-compare -Wno-conversion -Wno-un
used-result -Wno-narrowing -Wno-attributes -Wno-unused-variable -Wno-array-bound
s -m64 -std=gnu89 -Wpointer-arith -Wbad-function-cast -Wstrict-prototypes -Wno-u
nused-function -O0 -include C:/MAME GitHub/src/osd/windows/winprefix.h -o ../../
../win64_mingw-gcc/obj/x64/Release/3rdparty/libflac/src/libFLAC/bitreader.o -MF
../../../win64_mingw-gcc/obj/x64/Release/3rdparty/libflac/src/libFLAC/bitreader.
d -c ../../../../3rdparty/libflac/src/libFLAC/bitreader.c, ...) failed.
make (e=2): The system cannot find the file specified.
flac.make:335: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdpa
rty/libflac/src/libFLAC/bitreader.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/libflac/src/libF
LAC/bitreader.o] Error 2
Makefile:28: recipe for target 'flac' failed
make[1]: *** [flac] Error 2
Compiling 3rdparty/lzma/C/7zBuf.c...
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-gc
c -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -D_
7ZIP_PPMD_SUPPPORT -D_7ZIP_ST -m64 --pipe -Wno-deprecated-declarations -O3 -fno-
strict-aliasing -Werror -Wno-unknown-pragmas -Wall -Wcast-align -Wundef -Wformat
-security -Wwrite-strings -Wno-sign-compare -Wno-conversion -Wno-unused-result -
Wno-narrowing -Wno-attributes -Wno-unused-variable -Wno-array-bounds -m64 -std=g
nu89 -Wpointer-arith -Wbad-function-cast -Wstrict-prototypes -include C:/MAME Gi
tHub/src/osd/windows/winprefix.h -o ../../../win64_mingw-gcc/obj/x64/Release/3rd
party/lzma/C/7zBuf.o -MF ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/lzma/
C/7zBuf.d -c ../../../../3rdparty/lzma/C/7zBuf.c, ...) failed.
make (e=2): The system cannot find the file specified.
7z.make:349: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdpart
y/lzma/C/7zBuf.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/lzma/C/7zBuf.o]
Error 2
make[2]: *** Waiting for unfinished jobs....
Compiling 3rdparty/lzma/C/7zBuf2.c...
process_begin: CreateProcess(NULL, c:\mingw\ming64-w64/bin/x86_64-w64-mingw32-gc
c -MMD -MP -DX64_WINDOWS_ABI -DPTR64=1 -DNDEBUG -DCRLF=3 -DLSB_FIRST -DFLAC__NO_
DLL -DNATIVE_DRC=drcbe_x64 -DLUA_COMPAT_APIINTCASTS -DWIN32 -Dmain=utf8_main -D_
7ZIP_PPMD_SUPPPORT -D_7ZIP_ST -m64 --pipe -Wno-deprecated-declarations -O3 -fno-
strict-aliasing -Werror -Wno-unknown-pragmas -Wall -Wcast-align -Wundef -Wformat
-security -Wwrite-strings -Wno-sign-compare -Wno-conversion -Wno-unused-result -
Wno-narrowing -Wno-attributes -Wno-unused-variable -Wno-array-bounds -m64 -std=g
nu89 -Wpointer-arith -Wbad-function-cast -Wstrict-prototypes -include C:/MAME Gi
tHub/src/osd/windows/winprefix.h -o ../../../win64_mingw-gcc/obj/x64/Release/3rd
party/lzma/C/7zBuf2.o -MF ../../../win64_mingw-gcc/obj/x64/Release/3rdparty/lzma
/C/7zBuf2.d -c ../../../../3rdparty/lzma/C/7zBuf2.c, ...) failed.
make (e=2): The system cannot find the file specified.
7z.make:353: recipe for target '../../../win64_mingw-gcc/obj/x64/Release/3rdpart
y/lzma/C/7zBuf2.o' failed
make[2]: *** [../../../win64_mingw-gcc/obj/x64/Release/3rdparty/lzma/C/7zBuf2.o]
Error 2
Makefile:31: recipe for target '7z' failed
make[1]: *** [7z] Error 2
makefile:355: recipe for target 'windows_x64' failed
make: *** [windows_x64] Error 2

Basically just a bunch of non-sensicle jibberish lol. I get the same, or roughly the same error message when trying to compile MESS as well, and I have ran make clean before hand.

My batch file looks like this (which was all working fine a few weeks ago)

MAME:

@echo off
set MINGW64=c:\mingw\ming64-w64
set path=c:\mingw\mingw64-w64\bin;c:\mingw\mingw64-w64\opt\bin;c:\mingw\mingw64-w64\Qt\bin;
make -j6 TARGET=mame
pause

MESS:

@echo off
set MINGW64=c:\mingw\ming64-w64
set path=c:\mingw\mingw64-w64\bin;c:\mingw\mingw64-w64\opt\bin;c:\mingw\mingw64-w64\Qt\bin;
make -j6 TARGET=mess
pause

I've added pause at the end so I can see what the error message is.

Again any help would be awesome!