Implement Sema::isExprCallable.

We can use this to produce nice diagnostics (and try to fixit-and-recover) in
various cases where we might see "MyFunction" instead of "MyFunction()". The
changes in SemaExpr are an example of how to use isExprCallable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130878 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed