ci: check for missing meson dependencies

Based on @eschwartz's https://codeberg.org/eli-schwartz/eschwartz-dev-scripts/src/branch/master/install-qa-check.d/50ninja-missingdeps

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37490>

.gitlab-ci/meson/build.sh

@@ -222,6 +222,17 @@ if [ "${RUN_MESON_TESTS}" = "true" ]; then
     LC_ALL=C.UTF-8 meson test --num-processes "${FDO_CI_CONCURRENT:-4}" --print-errorlogs ${MESON_TEST_ARGS}
 fi
 
+uncollapsed_section_switch meson-missingdeps "meson: check for missing dependencies"
+
+if ! missingdeps=$(ninja -t missingdeps); then
+  # phony rules are false positives
+  missingdeps=$(grep -vF '(generated by phony)' <<< "$missingdeps")
+  if grep -qE '^Missing dep:' <<< "$missingdeps"; then
+    echo "$missingdeps"
+    exit 1
+  fi
+fi
+
 section_switch meson-install "meson: install"
 ninja install
 cd ..