Support macos amd64 cross compilation

.github/workflows/ci.yml

@@ -1010,6 +1010,65 @@ jobs:
           tag: ${{ env.TOIT_VERSION }}
           overwrite: true
 
+  test_cross:
+    runs-on: ${{ matrix.os }}
+    needs: [prereqs, combine]
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+
+    steps:
+      - name: Set up constants
+        id: constants
+        shell: bash
+        run: |
+          if [[ "$RUNNER_OS" == "Linux" ]]; then
+            echo "artifact=toit-linux-x64.tar.gz" >> $GITHUB_OUTPUT
+            echo "artifact_name=Linux-build-combined" >> $GITHUB_OUTPUT
+          elif [[ "$RUNNER_OS" == "macOS" ]]; then
+            echo "artifact=toit-macos.tar.gz" >> $GITHUB_OUTPUT
+            echo "artifact_name=macOS-build-unsigned-combined" >> $GITHUB_OUTPUT
+          elif [[ "$RUNNER_OS" == "Windows" ]]; then
+            echo "artifact=toit-windows.tar.gz" >> $GITHUB_OUTPUT
+            echo "artifact_name=Windows-build-unsigned-combined" >> $GITHUB_OUTPUT
+          else
+            echo "UNSUPPORTED RUNNER: $RUNNER_OS"
+            exit 1
+          fi
+
+      - uses: actions/download-artifact@v7
+        with:
+          name: ${{ steps.constants.outputs.artifact_name }}
+
+      - name: Unpack SDK
+        shell: bash
+        run: |
+          tar x -zf ${{ steps.constants.outputs.artifact }}
+
+      - name: Test cross compilation
+        shell: bash
+        run: |
+          echo 'main: print "hello world"' > hello.toit
+          for out_os in linux darwin windows; do
+            for out_arch in amd64 aarch64 arm arm64 riscv64; do
+              # The windows build of the compiler needs .exe
+              COMPILER="toit/bin/toit"
+              if [[ "$RUNNER_OS" == "Windows" ]]; then COMPILER="toit/bin/toit.exe"; fi
+
+              VESSEL_ARCH=$out_arch
+              if [[ "$out_os" == "darwin" && "$out_arch" == "amd64" ]]; then
+                # The compiler automatically uses the fat binary in aarch64 for amd64 darwin.
+                VESSEL_ARCH="aarch64"
+              fi
+
+              if [ -d "toit/lib/toit/vessels/$out_os/$VESSEL_ARCH" ]; then
+                echo "Cross-compiling for $out_os/$out_arch"
+                ./$COMPILER compile --os=$out_os --arch=$out_arch -o hello_out hello.toit
+              fi
+            done
+          done
+
   sign_windows:
     runs-on: windows-latest
     needs: [prereqs, combine]

src/compiler/executable.cc

@@ -94,6 +94,10 @@ int create_executable(const char* out_path,
   }
   if (os != null) {
     builder.join(os);
+    if (strcmp(os, "darwin") == 0 && strcmp(arch, "amd64") == 0) {
+      // We now have fat binaries that combine arm64 and x64.
+      arch = "aarch64";
+    }
   }
   if (arch != null) {
     // If we have an arch, we should always have an os, but we