S_setlocale_2008_i(): Use single newlocale() if available

On some platforms the newlocale() libc function when setting LC_ALL can
handle an input locale that sets some categories to one thing; and
others to another; etc.  On such platforms, we don't have to loop
through all categories individually.

This commit changes to use that if the #define indicating its
availability is set.

locale.c

@@ -1944,6 +1944,11 @@ S_bool_setlocale_2008_i(pTHX_
     }
 
 #  endif
+#  ifdef NEWLOCALE_HANDLES_DISPARATE_LC_ALL
+
+    const bool need_loop = false;
+
+#  else
 
     bool need_loop = false;
     const char * new_locales[LC_ALL_INDEX_] = { NULL };
@@ -1978,6 +1983,7 @@ S_bool_setlocale_2008_i(pTHX_
         }
     }
 
+#  endif
 #  ifdef HAS_GLIBC_LC_MESSAGES_BUG
 
     /* For this bug, if the LC_MESSAGES locale changes, we have to do an
@@ -2094,8 +2100,17 @@ S_bool_setlocale_2008_i(pTHX_
          * you can set PERL_DESTRUCT_LEVEL=2 to cause it to be freed.
          */
 
+#  ifdef NEWLOCALE_HANDLES_DISPARATE_LC_ALL
+
+        /* Some platforms have a newlocale() that can handle disparate LC_ALL
+         * input, so on these a single call to newlocale() always works */
+#  else
+
         /* If a single call to newlocale() will do */
         if (! need_loop)
+
+#  endif
+
         {
             new_obj = newlocale(mask, new_locale, basis_obj);
             if (! new_obj) {
@@ -2118,6 +2133,9 @@ S_bool_setlocale_2008_i(pTHX_
 
             update_PL_curlocales_i(index, new_locale, caller_line);
         }
+
+#  ifndef NEWLOCALE_HANDLES_DISPARATE_LC_ALL
+
         else {  /* Need multiple newlocale() calls */
 
             /* Loop through the individual categories, setting the locale of
@@ -2176,6 +2194,9 @@ S_bool_setlocale_2008_i(pTHX_
                 freelocale(entry_obj);
             }
         }
+
+#  endif    /* End of newlocale can't handle disparate LC_ALL input */
+
     }
 
 #  undef DEBUG_NEW_OBJECT_CREATED