type_traits: fix build with GCC

GCC 5 introduced __is_trivially_copyable for implementing
std::is_trivially_copyable.  However, gcc does not report it through
__has_feature.  Perform a version check instead.  Repairs the build with
GCC.

Author: compnerd

include/swift/Basic/type_traits.h

@@ -33,7 +33,7 @@ struct IsTriviallyCopyable {
 #if _LIBCPP_VERSION || SWIFT_COMPILER_IS_MSVC
   // libc++ and MSVC implement is_trivially_copyable.
   static const bool value = std::is_trivially_copyable<T>::value;
-#elif __has_feature(is_trivially_copyable)
+#elif __has_feature(is_trivially_copyable) || __GNUC__ >= 5
   static const bool value = __is_trivially_copyable(T);
 #else
 #  error "Not implemented"
@@ -45,7 +45,7 @@ struct IsTriviallyConstructible {
 #if _LIBCPP_VERSION || SWIFT_COMPILER_IS_MSVC
   // libc++ and MSVC implement is_trivially_constructible.
   static const bool value = std::is_trivially_constructible<T>::value;
-#elif __has_feature(has_trivial_constructor)
+#elif __has_feature(has_trivial_constructor) || __GNUC__ >= 5
   static const bool value = __has_trivial_constructor(T);
 #else
 #  error "Not implemented"
@@ -57,7 +57,7 @@ struct IsTriviallyDestructible {
 #if _LIBCPP_VERSION || SWIFT_COMPILER_IS_MSVC
   // libc++ and MSVC implement is_trivially_destructible.
   static const bool value = std::is_trivially_destructible<T>::value;
-#elif __has_feature(has_trivial_destructor)
+#elif __has_feature(has_trivial_destructor) || __GNUC__ >= 5
   static const bool value = __has_trivial_destructor(T);
 #else
 #  error "Not implemented"