http://gcc.gnu.org/ml/gcc-patches/2014-03/msg00106.html

        * opts.h (CL_PCH_IGNORE): Define.
        * targhooks.c (option_affects_pch_p):
        Return false for options that have CL_PCH_IGNORE set.
        * opt-functions.awk: Process PchIgnore.
        * doc/options.texi: Document PchIgnore.
        * config/arc/arc.opt (misize): Add PchIgnore property.
        * config/arc/arc.md (casesi_load) <length attribute alternative 0>:
        Mark as varying.