The testcshared test.bash was rewritten in Go, but the rewritten script
broke on Android. Make the tests run on Android again by:

- Restoring the LD_LIBRARY_PATH path (.).
- Restoring the Android specific C flags (-pie -fuse-ld=gold).
- Adding runExe to run test executables. All other commands must run on
the host.

Fixes #21513.

Change-Id: I3ea617a943c686b15437cc5c118e9802a913d93a
Reviewed-on: https://go-review.googlesource.com/57290
Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>