DOS/Windows-related changes in the include subdirectory

[Eli Zaretskii]

> It might be nice to use the same set of macros that gcc uses, rather
> than invent our own.  In gcc.c I see things like PATH_SEPARATOR,
> DIR_SEPARATOR, DIR_SEPARATOR_2, IS_DIR_SEPARATOR,
> HAVE_DOS_BASED_FILESYSTEM.

Sorry, I didn't know GCC was special in this aspect.  I used the names
used by other packages, like Texinfo, Web2C and some others.

If you want me to change the definitions, please send me the
definitions from the GCC sources (I don't have them installed).
Please also tell me what to do in case some of the definitions I used
don't have any equivalents in GCC (the above names seem to indicate
that e.g. IS_ABSOLUTE and FILENAME_CMP aren't used by GCC).