locale.c: Avoid unnecessary locale recalculation

In these functions, we already know the locale, so pass it to the called
function instead of NULL, so that that function won't have to
recalculate it.

locale.c

@@ -10228,11 +10228,13 @@ Perl_my_strerror(pTHX_ const int errnum, utf8ness_t * utf8ness)
                matches */
         locale_t cur = duplocale(use_curlocale_scratch());
 
-        cur = newlocale(LC_CTYPE_MASK, querylocale_c(LC_MESSAGES), cur);
+        const char * locale = querylocale_c(LC_MESSAGES);
+        cur = newlocale(LC_CTYPE_MASK, locale, cur);
         errstr = savepv(strerror_l(errnum, cur));
         *utf8ness = get_locale_string_utf8ness_i(errstr,
                                                  LOCALE_UTF8NESS_UNKNOWN,
-                                                 NULL, LC_MESSAGES_INDEX_);
+                                                 locale,
+                                                 LC_MESSAGES_INDEX_);
         freelocale(cur);
     }
 
@@ -10339,7 +10341,8 @@ Perl_my_strerror(pTHX_ const int errnum, utf8ness_t * utf8ness)
     LOCALE_UNLOCK;
 
     *utf8ness = get_locale_string_utf8ness_i(errstr, LOCALE_UTF8NESS_UNKNOWN,
-                                             NULL, LC_MESSAGES_INDEX_);
+                                             desired_locale,
+                                             LC_MESSAGES_INDEX_);
     DEBUG_STRERROR_RETURN(errstr, utf8ness);
 
     SAVEFREEPV(errstr);