Add a new `coverage-unit-tests` make target that builds the unit tests for code coverage, runs the tests, and generates a coverage report. Signed-off-by: Paul Fagerburg <pfagerburg@google.com> Change-Id: I6ea780ee9e246c0bb8c35b8e0de4252431dabbff Reviewed-on: https://review.coreboot.org/c/coreboot/+/52444 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Jakub Czapiga <jacz@semihalf.com>