Implement template instantiation for several more kinds of expressions:

Implement template instantiation for several more kinds of expressions:
  - C++ function casts, e.g., T(foo)
  - sizeof(), alignof()

More importantly, this allows us to verify that we're performing
overload resolution during template instantiation, with
argument-dependent lookup and the "cached" results of name lookup from
the template definition.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@66947 91177308-0d34-0410-b5e6-96231b3b80d8