cpp.texi: Document #pragma GCC dependency
* cpp.texi: Document #pragma GCC dependency
* cppfiles.c (open_include_file): Set date to unknown.
(_cpp_compare_file_date): New function.
(read_include_file): Set file date.
* cpphash.h (struct include_file): Add date member.
(_cpp_compare_file_date): Prototype.
* cpplib.c (parse_include): Add trail parameter. Adjust.
(do_include): Adjust parse_include call.
(do_import): Likewise.
(do_include_next): Likewise.
(gcc_pragmas): Add dependency pragma.
(do_pragma_dependancy): New pragma.
From-SVN: r34808