test: fix inline.go test for linux-amd64-noopt

math.Float32bits was not being inlined across package boundaries.
Create a private func that can be inlined with -l.

Change-Id: Ic50bf4727dd8ade09d011eb204006b7ee88db34a
Reviewed-on: https://go-review.googlesource.com/c/go/+/295989


Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>