[clang] [clang][FMV] Pass the '+fmv' target-feature when FMV is enabled. (PR #87942)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

> @labrinea @jroelofs Is there anything that still needs to be done here or can this be merged?

Currently the dependent PR #87939 is on hold. Unless it moves forward this PR is not needed.

https://github.com/llvm/llvm-project/pull/87942