x/build: add Solaris amd64 release builder to dashboard
x/build: add Solaris amd64 release builder to dashboard

Fixes golang/go#20949

Change-Id: I4f85ee76783a1240a2ebd4a2a1f167ab849fcebe
Reviewed-on: https://go-review.googlesource.com/47811
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build