[clang] [clang][Driver]Fix opencl -cl-fast-relaxed-math flag to have similar behaviour as ffast-math (PR #208709)

[Wenju He via cfe-commits]

wenju-he wrote:

> Raw CC1 invocations don't have an expectation of stability?

Yes, but -ffast-math still has old behavior in cc1. This PR only changes -cl-fast-relaxed-math.
If everything is moved to driver, it will be very difficult for cc1 users that embed clang as frontend.

https://github.com/llvm/llvm-project/pull/208709