* c-lex.c (init_c_lex): Request #define / #undef callbacks
        for verbose DWARF[2] debugging.
        (cb_define, cb_undef): The new callbacks.
        * toplev.h (debug_define, debug_undef): Make const correct.
        * toplev.c (debug_define, debug_undef): Similarly.  Do not
        perform the verbosity tests here anymore.

From-SVN: r38756