locale.c: Use low level macros at low level

Implementing Perl_setlocale, we can safely use the internal macros that
the public ones expand to call, without the overhead those public macros
impose (which they do to be more immune from improper calls from outside
code).

locale.c

@@ -2240,7 +2240,7 @@ Perl_setlocale(const int category, const char * locale)
 #  ifdef USE_LOCALE_NUMERIC
 #    ifdef LC_ALL
 
-    DECLARATION_FOR_LC_NUMERIC_MANIPULATION;
+        bool toggled = FALSE;
 
 #    endif
 
@@ -2253,25 +2253,29 @@ Perl_setlocale(const int category, const char * locale)
             return PL_numeric_name;
         }
 
-#  ifdef LC_ALL
+#  endif
+#  if defined(USE_LOCALE_NUMERIC) && defined(LC_ALL)
 
         /* For an LC_ALL query, switch back to the underlying numeric locale
          * (if we aren't there already) so as to get the correct results.  Our
          * records for all the other categories are valid without switching */
-        if (category == LC_ALL) {
-            STORE_LC_NUMERIC_FORCE_TO_UNDERLYING();
+        if (category == LC_ALL && ! PL_numeric_underlying) {
+            set_numeric_underlying();
+            toggled = TRUE;
         }
 
 #  endif
-#  endif    /* End of has LC_NUMERIC */
 
-        retval = save_to_buffer(querylocale_r(category),
-                                &PL_setlocale_buf, &PL_setlocale_bufsize, 0);
+        retval = querylocale_r(category);
 
-#  if defined(USE_LOCALE_NUMERIC) && defined(LC_ALL)
+#  ifdef LC_ALL
 
-        if (category == LC_ALL) {
-            RESTORE_LC_NUMERIC();
+        if (toggled) {
+
+            /* This toggling back could destroy 'retval' */
+            retval = save_to_buffer(retval,
+                                    &PL_setlocale_buf, &PL_setlocale_bufsize, 0);
+            set_numeric_standard();
     }
 
 #  endif