implement uselocale function (minimal)

src/internal/pthread_impl.h

@@ -12,6 +12,7 @@
 #include <setjmp.h>
 #include <string.h>
 #include <time.h>
+#include <locale.h>
 #include "libc.h"
 #include "syscall.h"
 #include "atomic.h"
@@ -44,6 +45,7 @@ struct pthread {
 	} robust_list;
 	int unblock_cancel;
 	int delete_timer;
+	locale_t locale;
 };
 
 struct __timer {

src/locale/uselocale.c

@@ -0,0 +1,10 @@
+#include "locale_impl.h"
+#include "pthread_impl.h"
+
+locale_t uselocale(locale_t l)
+{
+	pthread_t self = pthread_self();
+	locale_t old = self->locale;
+	if (l) self->locale = l;
+	return old;
+}