AnyOverlap and InexactOverlap implement checks for the aliasing
requirements defined by the crypto/cipher interfaces. Apply them to all
implementations as the actual requirement could be architecture-dependent
and user code should not rely on undefined behavior.

Updates golang/go#21624

Change-Id: I465de02fb3fec4e0c6f1fdee1ef6ae7ed5abff10
Reviewed-on: https://go-review.googlesource.com/112236Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>