clang-cl support.

[API92]

Tested with clang-cl.exe on amd64 and x86.

[darealshinji]

This part at the bottom:

#if defined(INCBIN_MSCL)
#  define INCTXT(NAME, FILENAME) \
     INCBIN_EXTERN(NAME)

Should be changed to this:

#if defined(INCBIN_MSCL)
#  define INCTXT(NAME, FILENAME) \
     INCBIN_EXTERN_2(char, NAME)

So that INCTXT() will always create const char * declarations.

[darealshinji]

I also think that INCBIN_ALIGN should be empty on original cl.exe because no assembler is used there and the compiler and linker will chose the right value?

#ifdef INCBIN_MSCL
#  define INCBIN_ALIGN /* __declspec(align(INCBIN_ALIGNMENT)) */
#else
#  define INCBIN_ALIGN __attribute__((aligned(INCBIN_ALIGNMENT)))
#endif

[API92]

@darealshinji I think all changes for cl.exe should be in another PR. This PR doesn't change behavior for cl.exe but only for clang-cl.exe.