[PATCH] aarch64: Optimized implementation of memrchr

[Wilco Dijkstra]

Hi Xuelei,

> Considering the excellent performance of memchr.S on glibc 2.30, the
> same algorithm is used to find chrin. Compared to memrchr.c, this
> method with memrchr.S achieves an average performance improvement
> of 58% based on benchtest and its extension cases.

For larger sizes it's more than 4 times faster than the generic version. The
implementation is very similar to memchr.S so this is OK.

Wilco