Readd the C++ ABI alignment handling logic

include/clang/Basic/TargetCXXABI.h

Index: include/clang/Basic/TargetCXXABI.h
diff --git a/include/clang/Basic/TargetCXXABI.h b/include/clang/Basic/TargetCXXABI.h
index 42a976b3afdeb420d92cd700c504cada36c3ce85..c0a72cd413385f9bf073ac6e7a51ce4037eeee25 100644
--- a/include/clang/Basic/TargetCXXABI.h
+++ b/include/clang/Basic/TargetCXXABI.h
@@ -146,6 +146,24 @@ public:
     llvm_unreachable("bad ABI kind");
   }
 
+  /// \brief Are pointers to member functions differently aligned?
+  bool arePointersToMemberFunctionsAligned() const {
+    switch (getKind()) {
+    case GenericARM:
+    case GenericAArch64:
+      // TODO: ARM-style pointers to member functions put the discriminator in
+      //       the this adjustment, so they don't require functions to have any
+      //       special alignment and could therefore also return false.
+    case GenericItanium:
+    case GenericMIPS:
+    case iOS:
+    case iOS64:
+    case Microsoft:
+      return true;
+    }
+    llvm_unreachable("bad ABI kind");
+  }
+
   /// \brief Is the default C++ member function calling convention
   /// the same as the default calling convention?
   bool isMemberFunctionCCDefault() const {