ci: restore custom Windows runner with hermetic LLVM 0.7.9 (#29143)

The custom Windows argument-comment-lint job was temporarily moved to
`windows-2022` in #28940 after hermetic LLVM source extraction failed on
the newer runner. This takes the upstream extraction fix so the job can
return to the intended custom runner.

This upgrades `llvm` to `0.7.9` and `rules_cc` to `0.2.18`, refreshes
the module lock, rebases the remaining Windows and custom libc++
patches, drops the obsolete symlink-extraction workaround, and restores
the `windows-x64` runner configuration.

Validation:

- Verified all LLVM patches apply cleanly against the `0.7.9` source.
- Built `@llvm-project//compiler-rt:clang_rt.builtins.static`.

.github/workflows/rust-ci.yml

@@ -173,8 +173,11 @@ jobs:
             runner: macos-15-xlarge
             timeout_minutes: 30
           - name: Windows
-            runner: windows-2022
+            runner: windows-x64
             timeout_minutes: 30
+            runs_on:
+              group: ${{ github.event.repository.name }}-runners
+              labels: ${{ github.event.repository.name }}-windows-x64
     steps:
       - name: Check whether argument comment lint should run
         id: argument_comment_lint_gate