runtime/msan: use different msan routine for copying
__msan_memmove records the fact that we're copying memory, and
actually does the copy. Use instead __msan_copy_shadow, which
records the fact that we're copying memory, but doesn't actually
do the copy itself.
We're doing the copy ourselves, so we don't need msan to do it also.
More importantly, msan doing the copy clobbers the target before
we issue the write barrier, which causes pointers to get lost.
Fixes #76138
Change-Id: I17aea739f9444de21fac2bbfd81e48534a39481d
Reviewed-on: https://go-review.googlesource.com/c/go/+/719020 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: t hepudds <thepudds1460@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Radu Berinde <radu@cockroachlabs.com> Reviewed-by: Ian Lance Taylor <iant@golang.org>