Summary:
Introduce a new form of `result_of` without function type encoding.
Rename and split `is_callable/is_nothrow_callable` into `is_invocable/is_nothrow_invocable/is_invocable_r/is_nothrow_invocable_r` (and associated types accordingly)
Change function type encoding of previous `is_callable/is_nothrow_callable` traits to conventional template type parameter lists.
Reviewers: EricWF, mclow.lists, bebuch
Reviewed By: EricWF, bebuch
Subscribers: lichray, bebuch, cfe-commits
Differential Revision: https://reviews.llvm.org/D38831
llvm-svn: 320509