Trigger a compilation error when LOG_TAG is not provided

When compiling for OS_GENERIC, lack of LOG_TAG causes a compilation error.
Most developement happens on Android, which compiles this without an
error. This patch triggers a compilation failure on Android when LOG_TAG is not
provided.

Bug: 28118588
Change-Id: I316aa01952fb88d77bbabb197c77e4287a3fc39b