Skip trivial-copyability Expected expectations under gcc49

Summary:
[Folly] Skip trivial-copyability `Expected` expectations under gcc49.

The focus is on gcc5+; all that is needed for now is to keep code compiling with gcc49, but not necessarily to ensure optimal trivial-copyability behavior.

Reviewed By: Orvid

Differential Revision: D8364392

fbshipit-source-id: b0062193c844509b6bf26ed632dd8e5d4bdf77d2

folly/test/ExpectedTest.cpp

@@ -612,6 +612,9 @@ struct WithConstructor {
   WithConstructor();
 };
 
+// libstdc++ with GCC 4.x doesn't have std::is_trivially_copyable
+#if (defined(__clang__) && !defined(_LIBCPP_VERSION)) || \
+    !(defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5)
 TEST(Expected, TriviallyCopyable) {
   // These could all be static_asserts but EXPECT_* give much nicer output on
   // failure.
@@ -627,15 +630,12 @@ TEST(Expected, TriviallyCopyable) {
       (is_trivially_copyable<Expected<std::string, E>>::value));
   EXPECT_FALSE(
       (is_trivially_copyable<Expected<int, std::string>>::value));
-// libstdc++ with GCC 4.x doesn't have std::is_trivially_copyable
-#if (defined(__clang__) && !defined(_LIBCPP_VERSION)) || \
-    !(defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5)
   EXPECT_TRUE(
       (is_trivially_copyable<Expected<WithConstructor, E>>::value));
-#endif
   EXPECT_TRUE(
       (is_trivially_copyable<Expected<Expected<int, E>, E>>::value));
 }
+#endif
 
 TEST(Expected, Then) {
   // Lifting