clang: suppress a warning
clang: suppress a warning

Use signed "char *" for string.

    lib/normalizer.c:660:51: warning: passing
          'const unsigned char *' to parameter of type 'const char *' converts
          between pointers to integer types with different sign [-Wpointer-sign]
            grn_tokenizer_is_tokenized_delimiter(ctx, s, ls, GRN_ENC_UTF8)) {
                                                      ^
    include/groonga/tokenizer.h:59:59: note: passing
          argument to parameter 'str_ptr' here
                                                  const char *str_ptr,
                                                              ^

redfigure/groonga,cosmo0920/groonga,redfigure/groonga,kenhys/groonga,groonga/groonga,cosmo0920/groonga,redfigure/groonga,kenhys/groonga,hiroyuki-sato/groonga,cosmo0920/groonga,groonga/groonga,hiroyuki-sato/groonga,groonga/groonga,myokoym/groonga,cosmo0920/groonga,kenhys/groonga,komainu8/groonga,naoa/groonga,naoa/groonga,redfigure/groonga,myokoym/groonga,redfigure/groonga,redfigure/groonga,myokoym/groonga,cosmo0920/groonga,hiroyuki-sato/groonga,kenhys/groonga,kenhys/groonga,hiroyuki-sato/groonga,komainu8/groonga,naoa/groonga,myokoym/groonga,komainu8/groonga,hiroyuki-sato/groonga,komainu8/groonga,kenhys/groonga,cosmo0920/groonga,myokoym/groonga,myokoym/groonga,cosmo0920/groonga,naoa/groonga,komainu8/groonga,groonga/groonga,myokoym/groonga,groonga/groonga,komainu8/groonga,komainu8/groonga,naoa/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,redfigure/groonga,naoa/groonga,groonga/groonga,myokoym/groonga,hiroyuki-sato/groonga,naoa/groonga,hiroyuki-sato/groonga,kenhys/groonga,hiroyuki-sato/groonga,groonga/groonga,cosmo0920/groonga,komainu8/groonga,redfigure/groonga