Init LookupResult::AmbiguityKind

We don't expect useful value there unless it's "ambiguous".
However we use read it for copying and moving, so we need either init the field
add login to avoid reading invalid values. Such reads trigger ubsan errors.

llvm-svn: 343150

clang/include/clang/Sema/Lookup.h

@@ -709,7 +709,9 @@ private:
 
   // Results.
   LookupResultKind ResultKind = NotFound;
-  AmbiguityKind Ambiguity; // ill-defined unless ambiguous
+  // ill-defined unless ambiguous. Still need to be initialized it will be
+  // copied/moved.
+  AmbiguityKind Ambiguity = {}; 
   UnresolvedSet<8> Decls;
   CXXBasePaths *Paths = nullptr;
   CXXRecordDecl *NamingClass = nullptr;