libc dlfcn.c: make dl_iterate_phdr() from libc more useful

Apparently there are applications that resolve dl_iterate_phdr from libc
and try to call the symbol. Our libc only provides stubs for dl* to
satisfy static linker or statically linked binaries, and is not prepared
to this situation.

Add a code to dso libc to find real dl_iterate_phdr and redirect the
call to it.

Reported by: yuri
PR: 272992
Sponsored by: The FreeBSD Foundation
MFC after: 1 week