util/tests: compile to something sensible in release builds

util/tests: compile to something sensible in release builds

assert()-based tests make no sense without asserts, so make sure asserts
are compiled in, even if the rest of the code has asserts turned off.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>