cmd/dist,cmd/link: enable PIE buildmode on openbsd/arm64
The PIE buildmode works correctly on openbsd/arm64, hence enable it.
Updates #59866
Change-Id: I2f3c2839893659391539fafa12891d64f867e189
Reviewed-on: https://go-review.googlesource.com/c/go/+/570375
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Joel Sing <joel@sing.id.au>