Pop only when pushed.

Signed-off-by: Matthias Schulz <mschulz@hilscher.com>
diff --git a/library/constant_time_impl.h b/library/constant_time_impl.h
index 793ded4..273d215 100644
--- a/library/constant_time_impl.h
+++ b/library/constant_time_impl.h
@@ -546,7 +546,7 @@
     return (mbedtls_ct_condition_t) (~x);
 }
 
-#ifdef __GNUC__
+#if __GNUC__ > 4
 /* Restore warnings for -Wredundant-decls on gcc */
     #pragma GCC diagnostic pop
 #endif