[ADT] Be less clever when using a nonce type for disambiguation.

Old compilers don't like constexpr, but we're only going to use this in one
place anyway: this file. Everyone else should go through PointerLikeTypeTraits.

Update to r261259.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261268 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/PointerEmbeddedInt.h

@@ -45,7 +45,9 @@ class PointerEmbeddedInt {
     Mask = static_cast<uintptr_t>(-1) << Bits
   };
 
-  static constexpr const struct RawValueTag {} RawValue = RawValueTag();
+  struct RawValueTag {
+    explicit RawValueTag() = default;
+  };
 
   friend class PointerLikeTypeTraits<PointerEmbeddedInt>;
 
@@ -86,10 +88,10 @@ class PointerLikeTypeTraits<PointerEmbeddedInt<IntT, Bits>> {
     return reinterpret_cast<void *>(P.Value);
   }
   static inline T getFromVoidPointer(void *P) {
-    return T(reinterpret_cast<uintptr_t>(P), T::RawValue);
+    return T(reinterpret_cast<uintptr_t>(P), typename T::RawValueTag());
   }
   static inline T getFromVoidPointer(const void *P) {
-    return T(reinterpret_cast<uintptr_t>(P), T::RawValue);
+    return T(reinterpret_cast<uintptr_t>(P), typename T::RawValueTag());
   }
 
   enum { NumLowBitsAvailable = T::Shift };