All uses of these have been converted to use runtime/internal/math
functions for overflow checking.

Fixes #21588

Change-Id: I0ba57028e471803dc7d445e66d77a8f87edfdafb
Reviewed-on: https://go-review.googlesource.com/c/144037
Run-TryBot: Martin Möhrmann <martisch@uos.de>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>