[Sema] Better static assert diagnostics for expressions involving temporaries/casts/....

Summary:
Handles expressions such as:
 - `std::is_const<T>()`
 - `std::is_const<T>()()`;
 - `std::is_same(decltype(U()), V>::value`;

Reviewers: aaron.ballman, Quuxplusone

Subscribers: cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D55552

llvm-svn: 349729