ci: Add build profiling job

This adds a GHA jobs to help analyze build times
and its regressions. It is based on `clangStdenv` with `-ftime-trace`
together with `ClangBuildAnalyzer` to prepare markdown summary for
individual components.

This also has the minor benefit of dogfooding CA and impure derivations.

.github/workflows/ci.yml

@@ -221,3 +221,26 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
       - uses: DeterminateSystems/magic-nix-cache-action@main
       - run: nix build -L --out-link ./new-nix && PATH=$(pwd)/new-nix/bin:$PATH MAX_FLAKES=25 flake-regressions/eval-all.sh
+
+  profile_build:
+    needs: tests
+    runs-on: ubuntu-24.04
+    timeout-minutes: 60
+    if: >-
+      github.event_name == 'push' &&
+      github.ref_name == 'master'
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+    - uses: ./.github/actions/install-nix-action
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        dogfood: true
+        extra_nix_config: |
+          experimental-features = flakes nix-command ca-derivations impure-derivations
+          max-jobs = 1
+    - uses: DeterminateSystems/magic-nix-cache-action@main
+    - run: |
+        nix build -L --file ./ci/gha/profile-build buildTimeReport --out-link build-time-report.md
+        cat build-time-report.md >> $GITHUB_STEP_SUMMARY