runtime: use type int to specify size for newarray

runtime: use type int to specify size for newarray

Consistently use type int for the size argument of
runtime.newarray, runtime.reflect_unsafe_NewArray
and reflect.unsafe_NewArray.

Change-Id: Ic77bf2dde216c92ca8c49462f8eedc0385b6314e
Reviewed-on: https://go-review.googlesource.com/22311
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Martin Möhrmann <martisch@uos.de>
TryBot-Result: Gobot Gobot <gobot@golang.org>