ENH: use memchr/memcmp for unit stride all/any

Improves performance of all() by 50% with GNU libc >= 2.15 on a SSE2
AMD chip, Intels performance should be unchanged.
Improves performance of any() by 25% with GNU libc on a SSE4 chip but
SSE2 AMD chips lose 25%, Intels SSE2 performance should be unchanged.

The obsolete handvectorized code in simd.inc.src could be improved to
the same performance via unrolling once and using pminub/pmaxub to save
one slow pmovmskb instruction but using the libc routine has the
advantage that it will make best use of the underlying hardware no
matter how numpy was compiled.