Add rawmemchr

Add rawmemchr

Marcus Shawcroft wrote:
> This patch appears to have been munged by the mail system, can you
> repost as an attachment please.

Sure, I've attached the patch.

Wilco

Add a simple rawmemchr implementation. Use strlen for rawmemchr(s, '\0') as it is the
fastest way to search for '\0', and use memchr with an infinite size for other cases.
This is 3x faster for large sizes.

ChangeLog:
2016-04-22  Wilco Dijkstra  <wdijkstr@arm.com>

        * newlib/libc/machine/aarch64/Makefile.in: Add rawmemchr.S and
        rawmemchr-stub.c.
        * newlib/libc/machine/aarch64/Makefile.am: Likewise.
        * newlib/libc/machine/aarch64/rawmemchr.S (rawmemchr): Add rawmemchr.
        * newlib/libc/machine/aarch64/rawmemchr-stub.c (rawmemchr): Likewise.