misc/cgo: add various solaris build lines

Change-Id: Ifd9ac7f5300232fb83c6350a787b5803adb96b48
Reviewed-on: https://go-review.googlesource.com/8263
Reviewed-by: Minux Ma <minux@golang.org>
diff --git a/misc/cgo/test/cthread_unix.c b/misc/cgo/test/cthread_unix.c
index 3f39c15..d29f2fc 100644
--- a/misc/cgo/test/cthread_unix.c
+++ b/misc/cgo/test/cthread_unix.c
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd openbsd
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
 
 #include <pthread.h>
 #include "_cgo_export.h"