[flang] Add atomic_define and atomic_ref to list of intrinsics

Add the atomic subroutines, atomic_define and atomic_ref, to the
list of intrinsic subroutines. Add a new function
CheckAtomicDefineAndRef to check that for each of these procedures,
that their value arguments are the same type as their atom
arguments, and that their 3rd argument is not coindexed.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D136206