Build all targets, except for CLI tools (mmcli, uml290), with special
flags needed for collecting code coverage information when the build has
been configured with --enable-code-coverage.
Three new targets are available in the top build directory:
- `check-code-coverage' runs the test suite and generates a code
coverage report,
- `code-coverage-capture' generates a code coverage report from already
collected data, which can come in handy when one wants to see code
paths touched by a particular test,
- `code-coverage-clean' removes the collected coverage data and the
generated reports.
