[Sema] Add MacroQualified case for FunctionTypeUnwrapper

This is a fix for PR43315. An assertion error is hit for this minimal example:

```
//clang -cc1 -triple x86_64-- -S tstVMStructRC-min.cpp
int (a b)();  // Assertion `Chunk.Kind == DeclaratorChunk::Function' failed.
```

This is because we do not cover the case in the FunctionTypeUnwrapper where it
receives a MacroQualifiedType. We have not run into this earlier because this
is a unique case where the __attribute__ contains both __cdecl__ and
__regparm__ (in that order), and we are compiling for x86_64. Changing the
architecture or the order of __cdecl__ and __regparm__ does not raise the
assertion.

Differential Revision: https://reviews.llvm.org/D67992

(cherry picked from commit e278c13)

clang/lib/Sema/SemaType.cpp

@@ -6325,7 +6325,8 @@ namespace {
       Pointer,
       BlockPointer,
       Reference,
-      MemberPointer
+      MemberPointer,
+      MacroQualified,
     };
 
     QualType Original;
@@ -6356,6 +6357,9 @@ namespace {
         } else if (isa<AttributedType>(Ty)) {
           T = cast<AttributedType>(Ty)->getEquivalentType();
           Stack.push_back(Attributed);
+        } else if (isa<MacroQualifiedType>(Ty)) {
+          T = cast<MacroQualifiedType>(Ty)->getUnderlyingType();
+          Stack.push_back(MacroQualified);
         } else {
           const Type *DTy = Ty->getUnqualifiedDesugaredType();
           if (Ty == DTy) {
@@ -6412,6 +6416,9 @@ namespace {
         return C.getParenType(New);
       }
 
+      case MacroQualified:
+        return wrap(C, cast<MacroQualifiedType>(Old)->getUnderlyingType(), I);
+
       case Pointer: {
         QualType New = wrap(C, cast<PointerType>(Old)->getPointeeType(), I);
         return C.getPointerType(New);

clang/test/Frontend/macro_defined_type.cpp

@@ -19,3 +19,7 @@ void Func() {
 struct A {
   _LIBCPP_FLOAT_ABI int operator()() throw(); // expected-warning{{'pcs' calling convention is not supported for this target}}
 };
+
+// Added test for fix for PR43315
+#define a __attribute__((__cdecl__, __regparm__(0)))
+int(a b)();