ztest: error out when building tests with no compiler optimizations

Many tests are known to fail when built and no compiler optimizations.
Add a CMake check to error out when building a ztest based test with no
optimization, ask not file issues about it but also adds an opt-out
option to bypass the error for tests are actually designed to work in
this setup.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>