TFB does not supports cross-compilation and thus arm builds yet. As a workaround the CppUTest dependency is used for these builds (arm-linux) environment, but that builds with EXTENSIONS=OFF. As a result mocking and some other features are not working.

See: https://review.trustedfirmware.org/c/TS/trusted-services/+/7787/comment/fb6e10db_8f07032b/