rtld: when immediate bind mode is requested, process irelocs in PLT
immediately after other PLT relocs.

Otherwise, if the object has relro page, we write to readonly page,
and we would need to use mprotect(2) two more times to fix it. Note
that resolve_object_ifunc() does nothing when called second time, so
there is no need to avoid existing call.

Reported and tested by: emaste
PR: 233333
Sponsored by: The FreeBSD Foundation
MFC after: 1 week