ci/build: handle build timeout ourselves to give more time to nightly LTO builds

GitLab doesn't (yet) support `timeout:` being a variable, so let's put
the real `timeout:` at the max timeout we want, and internally use
another timeout (using coreutils' `timeout`) that we _can_ set using
a variable.

With that, we can set a 1h timeout on nightly LTO builds while keeping
our tighter 30min timeout the rest of the time.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31846>

.gitlab-ci.yml

@@ -46,6 +46,11 @@ workflow:
     - if: &is-fork-push $CI_PROJECT_NAMESPACE != "mesa" && $CI_PIPELINE_SOURCE == "push"
     # nightly pipeline
     - if: &is-scheduled-pipeline $CI_PIPELINE_SOURCE == "schedule"
+      variables:
+        # (some) nightly builds perform LTO, so they take much longer than the
+        # short timeout allowed in other pipelines.
+        # Note: 0 = infinity = gitlab's job `timeout:` applies, which is 1h
+        BUILD_JOB_TIMEOUT_OVERRIDE: 0
     # pipeline for direct pushes that bypassed the CI
     - if: &is-direct-push $CI_PROJECT_NAMESPACE == "mesa" && $CI_PIPELINE_SOURCE == "push" && $GITLAB_USER_LOGIN != "marge-bot"
       variables:

.gitlab-ci/build/gitlab-ci.yml

@@ -3,14 +3,15 @@
   extends: .container+build-rules
   # Cancel job if a newer commit is pushed to the same branch
   interruptible: true
+  variables:
     # Build jobs don't take more than 1-3 minutes. 5-8 min max on a fresh runner
     # without a populated ccache.
     # These jobs are never slow, either they finish within reasonable time or
     # something has gone wrong and the job will never terminate, so we should
     # instead timeout so that the retry mechanism can kick in.
-  # A few exception are made, see `timeout:` overrides in the rest of this
-  # file.
-  timeout: 30m
+    # A few exception are made, see overrides in the rest of this file.
+    BUILD_JOB_TIMEOUT: 30m
+  timeout: 1h
   # We don't want to download any previous job's artifacts
   dependencies: []
   artifacts:
@@ -60,7 +61,7 @@
   variables:
     LLVM_VERSION: 15
   script:
-    - &meson-build .gitlab-ci/meson/build.sh
+    - &meson-build timeout --verbose ${BUILD_JOB_TIMEOUT_OVERRIDE:-$BUILD_JOB_TIMEOUT} .gitlab-ci/meson/build.sh
 
 
 # Make sure this list stays the same as all the jobs with