Go doesn't guarantee that the result of floating point operations will
be the same on different architectures. It was not stated in the
documentation, that can lead to confusion.

Fixes #18354

Change-Id: Idb1b4c256fb9a7158a74256136eca3b8ce44476f
Reviewed-on: https://go-review.googlesource.com/34938Reviewed-by: Ian Lance Taylor <iant@golang.org>