runtime: add vgetrandom lock rank

runtime: add vgetrandom lock rank

vgetrandomGetState can call malloc, so this is not a leaf lock.

Our staticlockrank builder doesn't support vgetrandom, so it didn't
catch this.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-staticlockranking
Change-Id: I6a6a636c36c9172e4ebf9493c10cb23cac29a13f
Reviewed-on: https://go-review.googlesource.com/c/go/+/677255
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>