gitlab-ci: add static analysis check

Similar to the formatting check job, take advantage of the `clang-tidy`
configuration we just created to add a new job running this tool.

Running `clang-tidy` requires the following:
* build dependencies must be present on the system so it can resolve the
  includes
* the build folder must be configured as it relies on the
  `compile_commands.json` to get build flags (such as the include paths)

This could be run in the `build` job, but it would make it harder to
understand the actual underlying issue, so this is executed as a new,
separate job, re-using the artifacts from the `build` job.

.gitlab-ci.yml

@@ -37,3 +37,13 @@ format:
     - apt-get update
     - apt-get -y install ${BUILD_DEPS} clang-format-${CLANG_VERSION}
     - ninja -C build clang-format-check
+
+check:
+  stage: check
+  dependencies:
+    - build
+  script:
+    - apt-get update
+    # clang-tidy needs all dependencies to be installed so it can inspect their headers
+    - apt-get -y install ${BUILD_DEPS} clang-tidy-${CLANG_VERSION}
+    - ninja -C build clang-tidy