Just like android/arm, android/arm64 refuses to execute non-PIE
binaries. In addition, starting from the M release (Marshmallow),
Android refuses to execute binaries with any text relocations
(this was just a warning in the L release). This makes "-shared"
necessary as well when building executables for Android.

Change-Id: Id8802de5be98ff472fc370f8d22ffbde316aaf1e
Reviewed-on: https://go-review.googlesource.com/16744Reviewed-by: Ian Lance Taylor <iant@golang.org>