[clang] [clang][fmv] Drop .ifunc from target_version's entrypoint's mangling (PR #81194)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

Looks like we've done something similar for `target_clones` to fix a linker issue: https://github.com/llvm/llvm-project/commit/cee5b8777fa98312b05bf8aa81554910a8f867c5. What is the motive in this case?

https://github.com/llvm/llvm-project/pull/81194