runtime: support valgrind (but not asan) in specialized malloc functions
We're adding this so that the compiler doesn't need to know about
valgrind since it's just implemented using a build tag.
Change-Id: I6a6a696452b0379caceca2ae4e49195016f7a90d
Reviewed-on: https://go-review.googlesource.com/c/go/+/708296 Reviewed-by: Michael Matloob <matloob@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Matloob <matloob@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>