TEMP(ci:windows-tools): baseline measurement for Option B rework — REVERT BEFORE MERGE

Re-applies the hooks removed in 7f8e255 to collect a warm-ccache
baseline on the current LLVM_BUILD_TOOLS=Off + force-build-llvm-config
approach. Provides a reference wall-clock for comparing the follow-up
rework (install-distribution + Rust-side flag move) in isolation.

1. `if: false` on the LLVM artifact cache restore → forces Build LLVM
   to run every push, even on warm artifact cache.
2. `save: true` on the ccache-action → populates ccache on PR events
   so a second push observes warm-ccache behaviour.

ccache scope for this PR (refs/pull/365/merge) is already warm from
the prior `save: true` window — two 965 MB Windows entries saved
2026-04-22, inside the 7-day TTL. So the first push after this commit
already measures the warm-ccache target configuration.

Revert before merge. End-state behaviour (artifact restore works,
ccache saves only on non-PR events) is what ships.

Author: nebasuke

.github/actions/build-llvm/action.yml

@@ -107,8 +107,11 @@ runs:
         KEY="${KEY}-args${{ steps.build-config.outputs.args-hash }}-${SHA}"
         echo "key=${KEY}" | tee -a "${GITHUB_OUTPUT}"
 
+    # TEMP(ci:windows-tools): forced-miss so Build LLVM always runs and the
+    # Windows tool-disable change is actually exercised. REVERT BEFORE MERGE.
     - name: Restore LLVM artifact cache
       id: llvm-artifact-cache
+      if: false
       uses: actions/cache/restore@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
       with:
         path: ${{ inputs.working-dir != '.' && format('{0}/target-llvm/target-final', inputs.working-dir) || 'target-llvm/target-final' }}
@@ -175,7 +178,7 @@ runs:
         append-timestamp: true
         max-size: "10G"
         verbose: 2
-        save: ${{ github.event_name != 'pull_request' }}
+        save: true # TEMP(ci:windows-tools): populate ccache on PR events so a follow-up push to this branch can measure warm-ccache + tool-disable. REVERT BEFORE MERGE to `${{ github.event_name != 'pull_request' }}`.
 
     - name: Build LLVM
       if: steps.llvm-artifact-cache.outputs.cache-hit != 'true'