ansidecl.h: Reorganize for readability...

include:
        * ansidecl.h: Reorganize for readability, remove documentation
        of obsolete macros, document PARAMS and VPARAMS.  Add new
        macros VA_OPEN, VA_CLOSE, and VA_FIXEDARG for nicer variadic
        function implementation.

gcc:
        * cpperror.c: Use VA_OPEN/VA_CLOSE/VA_FIXEDARG throughout.

From-SVN: r45011