cmd/go: pass -X64 to ar on aix/ppc64
cmd/go: pass -X64 to ar on aix/ppc64

On aix/ppc64, ar tool must always have -X64 argument if it aims to
create 64 bits archives.

This commit also adds the -D flag handler when calling ar with
gccgotoolchain, to match gccgo version.

Change-Id: I1f5750f8f64a7073780d283567f0b60fc7fa5b97
Reviewed-on: https://go-review.googlesource.com/c/go/+/164417
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

nawawi/go,josharian/go,CAFxX/go,cloudflare/go,akutz/go,golang/go,CAFxX/go,CAFxX/go,akutz/go,akutz/go,akutz/go,akutz/go,CAFxX/go,CAFxX/go,golang/go,golang/go,josharian/go,josharian/go,nawawi/go,cloudflare/go,akutz/go,cloudflare/go,josharian/go,golang/go,akutz/go,golang/go,nawawi/go,josharian/go,CAFxX/go,golang/go,josharian/go,cloudflare/go,josharian/go,CAFxX/go,CAFxX/go,akutz/go,josharian/go,nawawi/go,nawawi/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,nawawi/go,golang/go,nawawi/go