Revert "Fix isPodLike for MSVC and use it in TypeHashing."

This reverts commit ac5edc198eb612f82293850c3488042708b1c5fa.

Apparently this doesn't cover all the bases, so some compilers
and standard libraries still think this is not trivially copyable
even though it is.  Reverting this back to an MSVC-only check for
now so that at least we have some coverage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320739 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/DebugInfo/CodeView/TypeHashing.h

@@ -132,10 +132,15 @@ struct GloballyHashedType {
     return Hashes;
   }
 };
-static_assert(isPodLike<GloballyHashedType>::value,
+#if defined(_MSC_VER)
+// is_trivially_copyable is not available in older versions of libc++, but it is
+// available in all supported versions of MSVC, so at least this gives us some
+// coverage.
+static_assert(std::is_trivially_copyable<GloballyHashedType>::value,
               "GloballyHashedType must be trivially copyable so that we can "
               "reinterpret_cast arrays of hash data to arrays of "
               "GloballyHashedType");
+#endif
 } // namespace codeview
 
 template <> struct DenseMapInfo<codeview::LocallyHashedType> {

include/llvm/Support/type_traits.h

@@ -30,9 +30,9 @@ namespace llvm {
 template <typename T>
 struct isPodLike {
   // std::is_trivially_copyable is available in libc++ with clang, libstdc++
-  // that comes with GCC 5, and MSVC.
+  // that comes with GCC 5.
 #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) ||      \
-    (defined(__GNUC__) && __GNUC__ >= 5) || defined(_MSC_VER)
+    (defined(__GNUC__) && __GNUC__ >= 5)
   // If the compiler supports the is_trivially_copyable trait use it, as it
   // matches the definition of isPodLike closely.
   static const bool value = std::is_trivially_copyable<T>::value;