* cppfiles.c (stack_include_file): Push zero-length buffers

    * cppfiles.c (stack_include_file): Push zero-length buffers
        in case of failure.  Return void, as we don't fail any more.
        (read_include_file): Check for files we shouldn't re-read.
        Don't return an error code; errors are implied by marking the
        file NEVER_REREAD.
        (_cpp_execute_include): Move the recursion and in-macro checks
        here.  Update for stack_include_file not failing.
        * cpplib.c (cpp_push_buffer): Always succeed, since
        _cpp_execute_include performs the recursion check.  Tidy up.
        * cpplib.h (cpp_push_buffer): Update prototype.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@38057 138bc75d-0d04-0410-961f-82ee72b054a4