Function multi-versioning: disable ifunc for ELF targets other than glibc/Android/FreeBSD

Generalize D127933 (Fuchsia special case) to other ELF targets. Ensure
that musl, NetBSD, OpenBSD, etc do not get ifunc codegen which is
unsupported in their rtld.

Link: https://discourse.llvm.org/t/does-ifunc-use-from-llvm-require-os-support/67628
Close: https://github.com/llvm/llvm-project/issues/64631