syscall: build export_unix_test.go on solaris

    
    Patch from Rainer Orth.
    
    Reviewed-on: https://go-review.googlesource.com/29436

From-SVN: r240285

gcc/go/gofrontend/MERGE

-57d120d75be87c2a0da67e750f16929891f1b8f4
+259b4fe81436a3836308f6c96e058edad07be338
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/syscall/export_unix_test.go

@@ -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
 
 package syscall