Not having much luck here. Same error since last Saturday actually. I'm on Windows 7 64-bit. Error occurs after updating to the latest source. I'm also getting a similar error about 3/4 of the way through. If I type make -j6 again it seems to continue on until it tries to link the MAME exe.

GCC 5.3.0 detected
Linking mame64.exe...
win32.cpp:(.text+0x160): multiple definition of `osd_get_clipboard_text()'
(.text+0x0): first defined here
../../../../mingw-gcc/bin/x64/Release/lib7z.a(7zIn.o):7zIn.c:(.text+0xe59): unde
fined reference to `SzFolder_Decode'
../../../../mingw-gcc/bin/x64/Release/lib7z.a(7zIn.o):7zIn.c:(.text+0x18bb): und
efined reference to `SzFolder_Decode'
collect2.exe: error: ld returned 1 exit status
mame.make:234: recipe for target '../../../../../mame64.exe' failed
make[2]: *** [../../../../../mame64.exe] Error 1
makefile:946: recipe for target 'mame' failed
make[1]: *** [mame] Error 2
makefile:900: recipe for target 'windows_x64' failed
make: *** [windows_x64] Error 2