cmd/dist: set buildmode=pie on Android
cmd/dist: set buildmode=pie on Android

Android refuses to run non-PIE binaries, a restriction already
encoded in the cmd/go tool's buildModeInit function. This CL adds
the necessary flags to cmd/dist to make ./make.bash run on an
Android device.

Change-Id: I162084f573befaa41dcb47a2b78448bce5b83d35
Reviewed-on: https://go-review.googlesource.com/c/go/+/170943
Run-TryBot: Elias Naur <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@eliasnaur.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

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