add cross-build workflow

.github/workflows/cross-build.yml

@@ -0,0 +1,43 @@
+name: llvm_cross_build
+on:
+  workflow_dispatch:
+    inputs:
+      llvm_mos_repo:
+        description: 'llvm-mos repo'
+        default: 'llvm-mos/llvm-mos'
+        type: string
+      llvm_mos_sdk_repo:
+        description: 'llvm-mos-sdk repo'
+        default: 'llvm-mos/llvm-mos-sdk'
+        type: string
+      llvm_mos_ref:
+        description: 'llvm-mos ref'
+        default: 'main'
+        type: string
+      llvm_mos_sdk_ref:
+        description: 'llvm-mos-sdk ref'
+        default: 'main'
+        type: string
+
+
+jobs:
+  amd64_image:
+    uses: ./.github/workflows/cross-build-llvm-mos.yml
+    with:
+      arch: amd64
+    secrets: inherit
+
+  arm64_image:
+    uses: ./.github/workflows/cross-build-llvm-mos.yml
+    with:
+      arch: arm64
+    secrets: inherit
+
+  final:
+    runs-on: ubuntu-latest
+    needs:
+      - amd64_image
+      - arm64_image
+    steps:
+      - name: hello
+        run: echo preparing multi-arch image