[ODRHash] Revert r307743 which reverted r307720

Reapply r307720 to allow processing of constructors and destructors.  Reuse
the diagnostics for CXXMethodDecl for them.

llvm-svn: 308077
diff --git a/clang/lib/AST/ODRHash.cpp b/clang/lib/AST/ODRHash.cpp
index c16f4f3..b191353 100644
--- a/clang/lib/AST/ODRHash.cpp
+++ b/clang/lib/AST/ODRHash.cpp
@@ -354,6 +354,8 @@
     default:
       return false;
     case Decl::AccessSpec:
+    case Decl::CXXConstructor:
+    case Decl::CXXDestructor:
     case Decl::CXXMethod:
     case Decl::Field:
     case Decl::Friend: