syscall: don't make //sys lines be doc comments

Cleans up godoc and makes it consistent. (some had it, some
didn't)

This still keeps the information there, though, for people
looking at the source directly.

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7324056

src/pkg/syscall/syscall_bsd.go

@@ -20,6 +20,7 @@ import (
 /*
  * Pseudo-system calls
  */
+
 // The const provides a compile-time constant so clients
 // can adjust to whether there is a working Getwd and avoid
 // even linking this function into the binary.  See ../os/getwd.go.