These are used by DIV[U] and MOD[U] assembly instructions.
Add a test in the stdlib so we actually exercise linking
to these routines.

Update #19507

Change-Id: I0d8e19a53e3744abc0c661ea95486f94ec67585e
Reviewed-on: https://go-review.googlesource.com/45703Reviewed-by: Cherry Zhang <cherryyz@google.com>