[Github][CI] Add Windows Premerge Job for Testing

This patch adds a windows premerge job for testing. We plan to enable this
by default soon once we have evaluated stability and have reasonably reason
to believe the system is reliable.

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -16,7 +16,7 @@ jobs:
     if: github.repository_owner == 'llvm'
     runs-on: llvm-premerge-linux-runners
     concurrency:
-      group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+      group: ${{ github.workflow }}-linux-${{ github.event.pull_request.number || github.sha }}
       cancel-in-progress: true
     container:
       image: ghcr.io/llvm/ci-ubuntu-22.04:latest
@@ -73,3 +73,21 @@ jobs:
           export CXX=/opt/llvm/bin/clang++
 
           ./.ci/monolithic-linux.sh "$(echo ${linux_projects} | tr ' ' ';')" "$(echo ${linux_check_targets})" "$(echo ${linux_runtimes} | tr ' ' ';')" "$(echo ${linux_runtime_check_targets})"
+  premerge-checks-windows:
+    if: github.repository_owner == 'llvm'
+    runs-on: llvm-premerge-windows-runners
+    concurrency:
+      group: ${{ github.workflow }}-windows-${{ github.event.pull_request.number || github.sha }}
+      cancel-in-progress: true
+    steps:
+      - name: Checkout LLVM
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 2
+      - name: Setup ccache
+        uses: hendrikmuhs/[email protected]
+      - name: Build and Test
+        continue-on-error: true
+        run: |
+          echo test
+