[Clang][OpenMP] Add the support for floating-point variables for specific atomic clauses
Currently when using `atomic update` with floating-point variables, if
the operation is add or sub, `cmpxchg`, instead of `atomicrmw` is emitted, as
shown in [1]. In fact, about three years ago, llvm-svn: 351850 added the
support for FP operations. This patch adds the support in OpenMP as well.
[1] https://godbolt.org/z/M7b4ba9na
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D124724