Implement all of P1825R0:
- implicitly movable entity can be an rvalue reference to non-volatile
automatic object.
- operand of throw-expression can be a function or catch-clause parameter
(support for function parameter has already been implemented).
- in the first overload resolution, the selected function no need to be
a constructor.
- in the first overload resolution, the first parameter of the selected
function no need to be an rvalue reference to the object's type.
This patch also removes the diagnostic `-Wreturn-std-move-in-c++11`.
Differential Revision: https://reviews.llvm.org/D88220
fbee4a0c79