diagnostics: update the grammar file

Let's use the fixits to actually update the grammar files.

* src/getargs.h, src/getargs.c (update_flag): New.
* src/fixits.h, src/fixits.c (fixits_run): New.
* src/main.c (main): Invoke fixits_run when --update is passed.
* tests/input.at (Deprecated directives): Check --update.

lib/.gitignore

@@ -315,3 +315,6 @@
 /xstrndup.h
 /xtime.c
 /xtime.h
+/rename.c
+/rmdir.c
+/same-inode.h