ci: Add lcov configuration to ignore g_return_*if_fail()/g_assert*()

While we can’t add markers to the macro implementations to cause lcov to
ignore them automatically, we can change our lcov configuration to
ignore all calls to them.

See https://github.com/linux-test-project/lcov/issues/44.

This causes all the un-takeable branches and un-reachable assertions to
be ignored by our code coverage, which bumps our statistics:
 • Lines: 74.9% → 74.8%
 • Functions: 82.3% → 82.3%
 • Branches: 53.3% → 64.2%

The rationale is that nobody should be testing programmer error
handling, as g_return_*if_fail() are used to guard against — so it’s not
reasonable to count missed branches like that in code coverage
statistics.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

.gitlab-ci/coverage-docker.sh

@@ -7,14 +7,14 @@ python3 ./.gitlab-ci/fixup-cov-paths.py _coverage/*.lcov
 
 for path in _coverage/*.lcov; do
     # Remove coverage from generated code in the build directory
-    lcov --rc lcov_branch_coverage=1 -r "${path}" '*/_build/*' -o "$(pwd)/${path}"
+    lcov --config-file .gitlab-ci/lcovrc -r "${path}" '*/_build/*' -o "$(pwd)/${path}"
     # Remove any coverage from system files
-    lcov --rc lcov_branch_coverage=1 -e "${path}" "$(pwd)/*" -o "$(pwd)/${path}"
+    lcov --config-file .gitlab-ci/lcovrc -e "${path}" "$(pwd)/*" -o "$(pwd)/${path}"
 done
 
 genhtml \
     --ignore-errors=source \
-    --rc lcov_branch_coverage=1 \
+    --config-file .gitlab-ci/lcovrc \
     _coverage/*.lcov \
     -o _coverage/coverage