Supressing GCC 4.7 warning for Optional

Summary:
Supressing the warning for GCC4.7, and supressing the error supressing
the warning in GCC4.6.

Test Plan: Compile, run unit tests on GCC4.6 and GCC4.7

Reviewed By: ldbrandy@fb.com

FB internal diff: D635982

folly/Optional.h

@@ -75,6 +75,8 @@ const None none = nullptr;
  */
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wuninitialized"
+#pragma GCC diagnostic ignored "-Wpragmas"
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
 
 template<class Value>
 class Optional : boost::totally_ordered<Optional<Value>,