CL 622042 added rand as a compiler builtin, but did not update builtinlist.
Also update the mkbuiltin comment to refer to the current file location,
and add a comment for runtime.rand that it is called from the compiler.
For #54766
Change-Id: I99d2c0bb0658da333775afe2ed0447265c845c82
Reviewed-on: https://go-review.googlesource.com/c/go/+/626755 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>