Suppress warnings generated by -Wwrite-strings

Here are suppressed warnings:

    src/fmt_fp.c: In function 'fmt_fp':
    src/fmt_fp.c:124:16: warning: initialization discards 'const' qualifier from pointer target type
         char *ss = (t&32)?"inf":"INF";
                    ^
    src/fmt_fp.c:125:17: warning: assignment discards 'const' qualifier from pointer target type
         if (y!=y) ss=(t&32)?"nan":"NAN";
                     ^
    mrbgems/mruby-string-ext/src/string.c: In function 'mrb_str_succ_bang':
    mrbgems/mruby-string-ext/src/string.c:302:27: warning: assignment discards 'const' qualifier from pointer target type
           if (e == b) prepend = "1";
                               ^
    mrbgems/mruby-string-ext/src/string.c:305:27: warning: assignment discards 'const' qualifier from pointer target type
           if (e == b) prepend = "a";
                               ^
    mrbgems/mruby-string-ext/src/string.c:308:27: warning: assignment discards 'const' qualifier from pointer target type
           if (e == b) prepend = "A";
                               ^
    mrbgems/mruby-bin-mruby/tools/mruby/mruby.c: In function 'main':
    mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:213:13: warning: assignment discards 'const' qualifier from pointer target type
         cmdline = args.cmdline ? args.cmdline : "-";
                 ^
    mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c: In function 'print_breakpoint':
    mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c:159:3: warning: initialization discards 'const' qualifier from pointer target type
       char* enable_letter[] = {BREAK_INFO_MSG_DISABLE, BREAK_INFO_MSG_ENABLE};
       ^
    mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c:159:3: warning: initialization discards 'const' qualifier from pointer target type

1 files changed, 1 insertions, 1 deletions

diff --git a/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c b/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c
index 442133f92..44ad9bb06 100644
--- a/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c
+++ b/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c
@@ -209,7 +209,7 @@ main(int argc, char **argv)
   /* Set $0 */
   zero_sym = mrb_intern_lit(mrb, "$0");
   if (args.rfp) {
-    char *cmdline;
+    const char *cmdline;
     cmdline = args.cmdline ? args.cmdline : "-";
     mrbc_filename(mrb, c, cmdline);
     mrb_gv_set(mrb, zero_sym, mrb_str_new_cstr(mrb, cmdline));