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

@@ -547,6 +547,7 @@ my @death_utf8 = mark_as_utf8(
  '/[\cネ]/' => "Character following \"\\c\" must be printable ASCII {#} m/[\\cネ{#}]/",
  '/\b{ネ}/' => "'ネ' is an unknown bound type {#} m/\\b{ネ{#}}/",
  '/\B{ネ}/' => "'ネ' is an unknown bound type {#} m/\\B{ネ{#}}/",
+ '/ネ(?<‿name>match)ネ/; #no latin1' => 'Group name must start with a non-digit word character {#} m/ネ(?<‿{#}name>match)ネ/',
 );
 push @death, @death_utf8;