ci: create clangarm64-build.yml

No GitHub-hosted ARM64 runners are available at the moment of writing,
but folks can leverage self-hosted runners of this architecture. This CI
pipeline comes in handy for forks of the git-for-windows/git project
that have such runners available. The pipeline can be kicked off
manually through a workflow_dispatch.

Signed-off-by: Dennis Ameling <dennis@dennisameling.com>

.github/workflows/clangarm64-build.yml

@@ -0,0 +1,25 @@
+name: CLANG build ARM64
+
+on:
+  workflow_dispatch:
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  clang-build:
+    runs-on: [Windows, ARM64]
+    env:
+      NO_PERL: 1
+    steps:
+      - uses: actions/checkout@v4
+      - uses: git-for-windows/setup-git-for-windows-sdk@v1
+        with:
+          flavor: makepkg-git
+          architecture: aarch64
+          # This assumes that the job is running on a self-hosted runner,
+          # in which case we need to cleanup SDK files.
+          cleanup: true
+      - name: Build Git CLANGARM64
+        run: make -j`nproc`