regcomp.c: Need to account for UTF group name

I found this by reading the code.  Prior to this commit, the parse
pointer was advanced by one byte; it should be advanced by one
character.  As long as the the character was ASCII, things worked.

I looked through the regcomp.c source for other mis-use of the macro
changed by this commit; none were obvious.

Author: khwilliamson

regcomp.c

@@ -2533,8 +2533,8 @@ S_reg_scan_name(pTHX_ RExC_state_t *pRExC_state, U32 flags)
                  && (advance = isWORDCHAR_utf8_safe( (U8 *) RExC_parse,
                                                      (U8 *) RExC_end)));
     } else {
-        RExC_parse_inc_by(1); /* so the <- from the vFAIL is after the offending
-                         character */
+        /* so the <- from the vFAIL is after the offending character */
+        RExC_parse_inc_safe();
         vFAIL("Group name must start with a non-digit word character");
     }
     sv_name = newSVpvn_flags(name_start, (int)(RExC_parse - name_start),

t/re/reg_mesg.t

@@ -486,6 +486,7 @@ my @death_utf8 = mark_as_utf8(
 
  '/ネ(?;ネ/' => 'Sequence (?;...) not recognized {#} m/ネ(?;{#}ネ/',
  '/ネ(?<;ネ/' => 'Group name must start with a non-digit word character {#} m/ネ(?<;{#}ネ/',
+ '/ネ(?<‿ネ/' => 'Group name must start with a non-digit word character {#} m/ネ(?<‿{#}ネ/',
  '/ネ(?\ixネ/' => 'Sequence (?\...) not recognized {#} m/ネ(?\{#}ixネ/',
  '/ネ(?^lu:ネ)/' => 'Regexp modifiers "l" and "u" are mutually exclusive {#} m/ネ(?^lu{#}:ネ)/',
 '/ネ(?lil:ネ)/' => 'Regexp modifier "l" may not appear twice {#} m/ネ(?lil{#}:ネ)/',