x86: Optimize strrchr-evex.S and implement with VMM headers

Optimization is:
1. Cache latest result in "fast path" loop with `vmovdqu` instead of
  `kunpckdq`.  This helps if there are more than one matches.

Code Size Changes:
strrchr-evex.S       :  +30 bytes (Same number of cache lines)

Net perf changes:

Reported as geometric mean of all improvements / regressions from N=10
runs of the benchtests. Value as New Time / Old Time so < 1.0 is
improvement and 1.0 is regression.

strrchr-evex.S       : 0.932 (From cases with higher match frequency)

Full results attached in email.

Full check passes on x86-64.