unix: add ioctlPtr with unsafe.Pointer arg on other unices

This is a followup for CL 340915 that adds ioctlPtr for all other
UNIX-like platforms.

For golang/go#44834

Change-Id: I0ecf84e53f13e5a8da736b3ba7f643262596d23c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/469315
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Dmitri Goutnik <dgoutnik@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

unix/syscall_aix.go

@@ -411,6 +411,7 @@ func (w WaitStatus) CoreDump() bool { return w&0x80 == 0x80 }
 func (w WaitStatus) TrapCause() int { return -1 }
 
 //sys	ioctl(fd int, req uint, arg uintptr) (err error)
+//sys	ioctlPtr(fd int, req uint, arg unsafe.Pointer) (err error)
 
 // fcntl must never be called with cmd=F_DUP2FD because it doesn't work on AIX
 // There is no way to create a custom fcntl and to keep //sys fcntl easily,