Fix various GCC mis-configurations for newer versions.

This patch goes through and enables C++11 and C++14 features for newer GCC's.
The main changes are:

1. Turn on variable templates. (Uses __cpp_variable_templates)
2. Assert atomic<Tp> is trivially copyable (Uses _GNUC_VER >= 501).
3. Turn on trailing return support for GCC. (Uses _GNUC_VER >= 404)
4. XFAIL void_t test for GCC 5.1 and 5.2. Fixed in GCC 6.

llvm-svn: 255585

1 files changed, 6 insertions, 0 deletions

diff --git a/libcxx/include/atomic b/libcxx/include/atomic
index b5d5a27b041..abec2a0b565 100644
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -552,6 +552,12 @@ typedef enum memory_order
 namespace __gcc_atomic {
 template <typename _Tp>
 struct __gcc_atomic_t {
+
+#if _GNUC_VER >= 501
+    static_assert(is_trivially_copyable<_Tp>::value,
+      "std::atomic<Tp> requires that 'Tp' be a trivially copyable type");
+#endif
+
   _LIBCPP_INLINE_VISIBILITY
 #ifndef _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS
     __gcc_atomic_t() _NOEXCEPT = default;