syscall: do not load native libraries on non-native powershell on arm

The powershell that currently ships on ARM Windows isn't native, so it
won't load native DLLs. So just skip the tests for now, and reenable it
if this ever changes.

Updates #46701.

Change-Id: I2559fdf13cb65d3ecdc4c6f6df7dec1b490b9651
Reviewed-on: https://go-review.googlesource.com/c/go/+/327210


TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>