Fix build failures with -DDEBUG.

        [BZ #19443]
        * crypt/crypt_util.c [DEBUG] (_ufc_prbits): Correct format string.
        [DEBUG] (_ufc_set_bits): Declare used.
        * iconv/gconv_dl.c [DEBUG]: Add a missing include directive.
        [DEBUG] (print_all): Declare used.
        * resolv/res_send.c [DEBUG] (__libc_res_nsend): Explicitly convert
        operands of the ternary ?: expression to target type.
        * stdlib/rshift.c [DEBUG] (mpn_rshift): Use assert() instead of
        calling the undeclared abort.
        * time/mktime.c [DEBUG] (DEBUG): Rename to DEBUG_MKTIME.