ASTMangler: fix mangling of generic ObjC types

The mangled context must match the number of type argument lists. This was not the case if the bound generic nominal had a special mangling context.

rdar://problem/53418742

Author: eeckstein

lib/AST/ASTMangler.cpp

@@ -1231,8 +1231,11 @@ void ASTMangler::appendBoundGenericArgs(Type type, bool &isFirstArgList) {
   } else {
     auto boundType = cast<BoundGenericType>(typePtr);
     genericArgs = boundType->getGenericArgs();
-    if (Type parent = boundType->getParent())
-      appendBoundGenericArgs(parent->getDesugaredType(), isFirstArgList);
+    if (Type parent = boundType->getParent()) {
+      GenericTypeDecl *decl = boundType->getAnyGeneric();
+      if (!getSpecialManglingContext(decl, UseObjCProtocolNames))
+        appendBoundGenericArgs(parent->getDesugaredType(), isFirstArgList);
+    }
   }
   if (isFirstArgList) {
     appendOperator("y");