* c-lex.c: s/change_file/file_change.
        * cpplib.h: Similarly.
        * cppmain.c: Similarly.
        * fix-header.c: Similarly.
        * cppfiles.c (stack_include_file): Pass the buffer location and
        size to cpp_push_buffer.  Generate the file_change callback,
        so that sysp is already set.
        * cpphash.h: Add _cpp_do_file_change.
        * cpplib.c (do_line): Set buffer->sysp directly. Generate the
        file_change callback after setting sysp.
        (_cpp_do_file_change): Handle FC_ENTER and the FC_RENAME exception
        here.
        (cpp_push_buffer): Don't generate a callback.  Clear sysp.
        (cpp_pop_buffer): Clean up logic.

From-SVN: r38357