syscall: reduce the set of architecture-dependent files on Plan 9

Change-Id: I98b172181c2fd85aa385341e28bc661dbc274252
Reviewed-on: https://go-review.googlesource.com/2167
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/syscall/syscall_plan9.go b/src/syscall/syscall_plan9.go
index f6a502b..7968708 100644
--- a/src/syscall/syscall_plan9.go
+++ b/src/syscall/syscall_plan9.go
@@ -140,12 +140,12 @@
 	return cstring(buf[:]), nil
 }
 
-//sys	pipe(p *[2]_C_int) (err error)
+//sys	pipe(p *[2]int32) (err error)
 func Pipe(p []int) (err error) {
 	if len(p) != 2 {
 		return NewError("bad arg in system call")
 	}
-	var pp [2]_C_int
+	var pp [2]int32
 	err = pipe(&pp)
 	p[0] = int(pp[0])
 	p[1] = int(pp[1])