Add "sqrt-intrisified" code generation tests for mips64 and 386, where
we weren't intrisifying math.Sqrt (see CL 96615 and CL 95916), and for
mips and amd64, which lacked sqrt intrinsics tests.

Change-Id: I0cfc08aec6eefd47f3cd7a5995a89393e8b7ed9e
Reviewed-on: https://go-review.googlesource.com/96716
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>