PowerPC: ifunc improvement for internal calls

This patch changes de default symbol redirection for internal call of
memcpy, memset, memchr, and strlen to the IFUNC resolved ones.  The
performance improvement is noticeable in algorithms that uses these
symbols extensible, like the regex functions.

This is a backport of 19c4bec0f43599eecc2f32de96ae179cd7d64053.