As discussed in CL 126621, these constants are already defined on Linux,
Darwin, FreeBSD and NetBSD. In order to ensure portability of existing
code using the syscall package, provide them for Solaris as well.

Change-Id: Id49f6991f36775b152b9c47b9923cd0a08053bcb
Reviewed-on: https://go-review.googlesource.com/130356
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>