PowerPC: Fix bzero definition for static libc for PPC32

This patch fixes an issue for powerpc32-fpu static build which fails
with an 'bzero' undefined reference. This patch adds bzero ifunc selector
for static builds and fixes the '__bzero_ppc' reference to default
memset symbol (since static memset build does not provide ifunc
selector).

Fixes BZ#16689.

Backport of dd3946c6.