PowerPC: strspn optimization for PPC64/POWER7

The optimization is achieved by following techniques:
  > hashing of needle.
  > hashing avoids scanning of duplicate entries in needle across the string.
  > initializing the hash table with Vector instructions (VSX) by quadword access.
  > unrolling when scanning for character in string across hash table.
PowerPC: Fix bzero definition for static libc for PPC64

This patch fixes an issue for powerpc64[le] static build where __bzero
is definied in multiple places (memset-ppc64.o and bzero.o). It is now
defined only in bzero.o and memset-ppc64.o only defined __bzero_ppc for
both dynamic and static library.

Fixes BZ#16683.

Backport of 4facea473059914983b7da8dd654c06b8e3dcc41
PowerPC: Fix strspn for static build

This patch makes the strspn ifunc selector build for static builds.

This is a backport of 27c7220a483bda576533aa9a0a9b42175644b1a1
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 dd3946c615184e1957a0cb09352cac72be5d6d5b.