depend-cleanup: bea89d038ac5 also moved memchr
Commit bea89d038ac5 added strlcat but also introduced a memchr wrapper
in the source tree rather than using the autogenerated one used for
AARCH64_STRING_FUNCS. Move memchr.S to MDSRS and add a cleanup rule for
the old wrapper.
Reviewed by: fuz
Sponsored by: The FreeBSD Foundation
Fixes: bea89d038ac5 ("lib/libc/aarch64/string: add strlcat SIMD implementation")
Differential Revision: https://reviews.freebsd.org/D48502