Adds AIX, DragonFly BSD, FreeBSD, NetBSD, OpenBSD and Solaris
to the list of operating systems where the GODEBUGCPU environment
variable will be parsed and interal/cpu features can be enabled
and disabled.

Updates #27218

Change-Id: I9cd99142e2a5147cb00ca57b581f049ea6ce8508
Reviewed-on: https://go-review.googlesource.com/c/145281Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Martin Möhrmann <martisch@uos.de>
TryBot-Result: Gobot Gobot <gobot@golang.org>