locale.c: localeconv() unconditional NUMERIC toggle

It is possible to lockout changing the LC_NUMERIC locale.  This is done
in some printf cases where a recursive call could get the radix
character wrong.  But localeconv(), which could be called during this
recursion on some platforms, toggles the locale briefly, without
affecting the surrounding calls; so it can do the toggle
unconditionally.

The previous commit merely moved the functionality of localeconv() from
POSIX.xs to locale.c.  This commit expands upon that.

locale.c

@@ -3024,19 +3024,31 @@ S_my_localeconv(pTHX)
 #  elif ! defined(TS_W32_BROKEN_LOCALECONV)  /* Next is regular lconv() */
 
     {
-        DECLARATION_FOR_LC_NUMERIC_MANIPULATION;
-
         /* There are so many locks because localeconv() deals with two
          * categories, and returns in a single global static buffer.  Some
          * locks might be no-ops on this platform, but not others.  We need to
          * lock if any one isn't a no-op. */
-        STORE_LC_NUMERIC_FORCE_TO_UNDERLYING();
+
+#    ifdef USE_LOCALE_NUMERIC
+
+        const char * orig_switched_locale = NULL;
+
+        LC_NUMERIC_LOCK(0);
+        orig_switched_locale = toggle_locale_c(LC_NUMERIC, PL_numeric_name);
+
+#    endif
 
         LOCALECONV_LOCK;
         retval = copy_localeconv(aTHX_ localeconv(), numeric_locale_is_utf8,
                                                     monetary_locale_is_utf8);
         LOCALECONV_UNLOCK;
-        RESTORE_LC_NUMERIC();
+
+#    ifdef USE_LOCALE_NUMERIC
+
+        restore_toggled_locale_c(LC_NUMERIC, orig_switched_locale);
+        LC_NUMERIC_UNLOCK;
+
+#    endif
 
         return retval;
     }
@@ -3063,11 +3075,15 @@ S_my_localeconv(pTHX)
         const char * save_global;
         const char * save_thread;
         bool restore_per_thread = FALSE;
-        DECLARATION_FOR_LC_NUMERIC_MANIPULATION;
 
-        /* Get to the proper per-thread locale state.  (The NUMERIC operations
-         * are no-ops if not paying attention to LC_NUMERIC) */
-        STORE_LC_NUMERIC_FORCE_TO_UNDERLYING();
+#    ifdef USE_LOCALE_NUMERIC
+
+        const char * orig_switched_locale = NULL;
+
+        LC_NUMERIC_LOCK(0);
+        orig_switched_locale = toggle_locale_c(LC_NUMERIC, PL_numeric_name);
+
+#    endif
 
         /* Save the per-thread locale state */
         save_thread  = savepv(querylocale_c(LC_ALL));
@@ -3101,7 +3117,12 @@ S_my_localeconv(pTHX)
         /* Restore the per-thread locale state */
         void_setlocale_c(LC_ALL, save_thread);
 
-        RESTORE_LC_NUMERIC();
+#    ifdef USE_LOCALE_NUMERIC
+
+        restore_toggled_locale_c(LC_NUMERIC, orig_switched_locale);
+        LC_NUMERIC_UNLOCK;
+
+#    endif
 
         Safefree(save_global);
         Safefree(save_thread);