unix: use C.ioctl in generated ioctlPtr

Changes made in CL 469315 broke aix syscall wrapper generaton by
generating a wrapper for a non-existent C.ioctl_ptr() function.

Change-Id: Iaeee3056480637c62a09ea61e2ec14793c59790a
Reviewed-on: https://go-review.googlesource.com/c/sys/+/470235
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Goutnik <dgoutnik@gmail.com>

unix/syscall_aix.go

@@ -411,7 +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)
+//sys	ioctlPtr(fd int, req uint, arg unsafe.Pointer) (err error) = ioctl
 
 // 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,