MS ABI: Properly call global delete when invoking virtual destructors

Summary:
The Itanium ABI approach of using offset-to-top isn't possible with the
MS ABI, it doesn't have that kind of information lying around.

Instead, we do the following:
- Call the virtual deleting destructor with the "don't delete the object
  flag" set.  The virtual deleting destructor will return a pointer to
  'this' adjusted to the most derived class.
- Call the global delete using the adjusted 'this' pointer.

Reviewers: rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5996

llvm-svn: 220993
diff --git a/clang/test/CodeGenCXX/microsoft-abi-thunks.cpp b/clang/test/CodeGenCXX/microsoft-abi-thunks.cpp
index f1602c8..843bc89 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-thunks.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-thunks.cpp
@@ -61,10 +61,10 @@
 
 C::C() {}  // Emits vftable and forces thunk generation.
 
-// CODEGEN-LABEL: define linkonce_odr x86_thiscallcc void @"\01??_EC@@W3AEPAXI@Z"(%struct.C* %this, i32 %should_call_delete)
+// CODEGEN-LABEL: define linkonce_odr x86_thiscallcc i8* @"\01??_EC@@W3AEPAXI@Z"(%struct.C* %this, i32 %should_call_delete)
 // CODEGEN:   getelementptr i8* {{.*}}, i32 -4
 // FIXME: should actually call _EC, not _GC.
-// CODEGEN:   call x86_thiscallcc void @"\01??_GC@@UAEPAXI@Z"
+// CODEGEN:   call x86_thiscallcc i8* @"\01??_GC@@UAEPAXI@Z"
 // CODEGEN: ret
 
 // CODEGEN-LABEL: define linkonce_odr x86_thiscallcc void @"\01?public_f@C@@W3AEXXZ"(%struct.C*