TEMP(ci:windows-tools): exercise tool-disable on PR — REVERT BEFORE MERGE

Mirrors the TEMP pattern from #360 but scoped to `build-llvm/action.yml`
only (this branch doesn't touch solc):

1. `if: false` on the LLVM artifact cache restore → forces Build LLVM to
   always run, so the Windows tool-disable change is actually exercised.
   Without this, the args-hash in the cache key only triggers miss on the
   first push (when no entry exists); subsequent pushes to this branch
   would hit the entry we just saved and skip the build, masking any
   regression.

2. `save: true` on the ccache-action → populates ccache in this branch's
   cache scope even on PR events, so a follow-up push can observe
   warm-ccache + tool-disable together (the actual target configuration).

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

Author: nebasuke

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

@@ -110,8 +110,11 @@ 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' }}
@@ -178,7 +181,7 @@ 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'