runtime: exclude allocation(s) from memmove/memclr benchmarking
The overhead for allocation is not significant but it should be excluded
from the memmove/memclr benchmarking anyway.
Change-Id: I7ea86d1b85b13352ccbff16f7510caa250654dab
Reviewed-on: https://go-review.googlesource.com/c/go/+/645576
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>