`\` fails, `/` works with generated 3d makefiles on Cygwin

[tahina-pro]

If I run make -C src/3d/tests/extern -j 4 on Cygwin with the mingw64 C compiler, I get the following error message:

make[3]: *** No rule to make target 'obj/TestWrapper.h', needed by 'obj/main.o'.

In fact, the handwritten "driver" Makefile is using / directory separators, but 3d on Windows generates obj/EverParse.Makefile with \ directory separators. If I use a unique directory separator (i.e. change \ into / in the generated obj/EverParse.Makefile, or alternatively change / into \ in the handwritten Makefile), then things seem to work well.

Things work well on Linux, where / is uniformly used.

[protz]

FYI / is a valid path separator on Windows, too