Attempt to fix a build bug report:
    
    ../../../../libgo/go/syscall/exec_linux.go:185:37: error: integer constant overflow
       _, err1 = raw_ioctl_ptr(sys.Ctty, TIOCSPGRP, unsafe.Pointer(&pgrp))
    
    Reviewed-on: https://go-review.googlesource.com/16539

From-SVN: r229674