makedef.pl: Skip locale thread symbols when necessary

Since 48d447b we don't have these symbols when building without
threads, so exclude them from the symbol list when setting up the
symbols for strict linkers.

makedef.pl

@@ -454,6 +454,11 @@ sub readvar {
 			 );
 }
 
+unless ($define{'USE_THREADS'}) {
+    ++$skip{Perl_thread_locale_init};
+    ++$skip{Perl_thread_locale_term};
+}
+
 unless ($define{USE_POSIX_2008_LOCALE})
 {
     ++$skip{$_} foreach qw(