socket: Improve fortify with clang

It improve fortify checks recv, recvfrom, poll, and ppoll.  The compile
and runtime hecks have similar coverage as with GCC.

Checked on aarch64, armhf, x86_64, and i686.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>