Not yet done ... Somebody experienced with bgfx needs to apply it. I am really not a bgfx expert. The compiled shaders are part of git. And this is were the fun begins. "make shaders" creates ~500 binary files which need to be committed. That's too much potential trouble.
I also found a fix for fs_xbr-lv3-noblend.cs:
Line 46 must be "#define CORNER_D 1", i.e. "1" needs to be added.