unsafe: say "functions like syscall.Syscall", not only Syscall

unsafe: say "functions like syscall.Syscall", not only Syscall

Fixes #68301

Change-Id: I9d7f623370705ab2ad4c49489b5a89162467f22a
Reviewed-on: https://go-review.googlesource.com/c/go/+/596936
Commit-Queue: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>