CL 9184 changed the runtime and syscall packages to link Solaris binaries
directly instead of using dlopen/dlsym but failed to update sys/unix to
reflect these changes.  This changes the Solaris port to use direct linking
as supported by Go 1.5.

Fixes golang/go#10086

Change-Id: I6747ed939775b18fd967f81853c7d84537aa3842
Reviewed-on: https://go-review.googlesource.com/13400Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>