c-lex.c: Move main_input_filename handling to FC_ENTER.

c-lex.c: Move main_input_filename handling to FC_ENTER.

        * c-lex.c: Move main_input_filename handling to FC_ENTER. Clean up.
        * cpperror.c (print_containing_files): Get right line number.
        (print_location): Output column of 1 if 0.
        * cppfiles.c (stack_include_file): cpp_push_buffer handles
        the callback.
        * cpphash.h (_cpp_do_file_change): No longer external.
        * cpplib.c (do_file_change): Now local to cpplib.c.
        (do_line): Fake a buffer stack for preprocessed files.
        (cpp_push_buffer): Create a file_change callback.  Handle faked
        buffers.
        (cpp_pop_buffer): Similarly.
        * cpplib.h: BUF_FAKE: New buffer type.
        * cppmain.c: Update to handle correct file renaming where a
        #line is the first line of the main file, and produce only
        the renamed file, not the original file, as output.

From-SVN: r38319