Use BUILD_NATIVE_TEST instead of BUILD_EXECUTABLE.

Use BUILD_NATIVE_TEST instead of BUILD_EXECUTABLE.

This will generate makefiles for our tools (bench, tests, gm, dm) using
the line "include $(BUILD_NATIVE_TEST)". This has been recommended by the
Android team, as it builds both 32 bit and 64 bit versions of the test.

Do not use LOCAL_MODULE_PATH, which is deprecated (see https://docs.google.com/a/google.com/document/d/1uLAuY7_KYGx1TSzJ9SXkyevT8qNpra2ZoIBkmCoq8VM/edit# ).

Corresponds to ag/498302 , which makes this change just for bench.

R=djsollen@google.com, halcanary@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/369673002