Fix initializing TypeOfTypeLoc

This fixes a crash in the RecursiveASTVisitor on such code
 __typeof__(struct F*) var[invalid];

The UnderlyingTInfo of a TypeOfTypeLoc was left uninitialized when
created from ASTContext::getTrivialTypeSourceInfo
This lead to a crash in RecursiveASTVisitor when trying to access it.

llvm-svn: 220562