locale.c: Add debug for MB_CUR_MAX

The latest MacOS release has locales that set this wrongly.  This isn't
the first time this has been a problem.  Add a debugging line that can
easily be enabled to check for problems that may arise in  the field.

Author: khwilliamson

locale.c

@@ -3851,6 +3851,9 @@ S_new_ctype(pTHX_ const char *newctype, bool force)
 
     const int mb_cur_max = MB_CUR_MAX;
 
+    DEBUG_Lv(PerlIO_printf(Perl_debug_log, "MB_CUR_MAX=%d, utf8?=%d\n",
+                                        mb_cur_max, PL_in_utf8_CTYPE_locale));
+
     if (mb_cur_max > 1 && ! PL_in_utf8_CTYPE_locale
 
             /* Some platforms return MB_CUR_MAX > 1 for even the "C" locale.