[GCC-XML] Re-enabling C parser

[Andrej Mitrovic]

Hi,

I'd like to give it a go at porting the XML routines so they work with
the C parser. I know the C++ parser can parse most C code but there's
a few differences here and there that might make it worthwhile for me
to use the C parser instead.

How exactly was GCC forced to always run the C++ compiler (cc1plus)?
cc1.exe is not generated at all so I guess it's disabled somewhere in
the CMake files?

Thanks.