tm.texi (TARGET_OPTION_OVERRIDE): Document.

tm.texi (TARGET_OPTION_OVERRIDE): Document.

        * doc/tm.texi (TARGET_OPTION_OVERRIDE): Document.
        (OVERRIDE_OPTIONS): Add note of obsolescence.
        Replace references with references to TARGET_OPTION_OVERRIDE.
        (Except for C_COMMON_OVERRIDE_OPTIONS, which remains similar to
         the macro).
        * targhooks.c (default_target_option_override): New function.
        * targhooks.h (default_target_option_override): Declare.
        * target.h (struct gcc_target): Add override member to
        target_option emmber.
        * toplev.c (process_options): Replace OVERRIDE_OPTIONS use with
        targetm.target_option.override call.
        * target-def.h (TARGET_OPTION_OVERRIDE): Define.
        (TARGET_OPTION_HOOKS): Add TARGET_OPTION_OVERRIDE.

From-SVN: r161538