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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> This PR broke cc1/CompilerInvocation path that bypasses driver entirely. Proposed a fix at #211768

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

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