gi: add macOS ARM64 builder

This means we can finally release native arm64 builds of TinyGo on
macOS!

Also update from macOS 11 to macOS 12, because macOS 11 is not supported
anymore.

.github/workflows/build-macos.yml

@@ -14,7 +14,17 @@ concurrency:
 jobs:
   build-macos:
     name: build-macos
-    runs-on: macos-11
+    strategy:
+      matrix:
+        # macos-12: amd64 (oldest supported version as of 05-02-2024)
+        # macos-14: arm64 (oldest arm64 version)
+        os: [macos-12, macos-14]
+        include:
+          - os: macos-12
+            goarch: amd64
+          - os: macos-14
+            goarch: arm64
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Install Dependencies
         shell: bash
@@ -33,7 +43,7 @@ jobs:
         uses: actions/cache/restore@v3
         id: cache-llvm-source
         with:
-          key: llvm-source-17-macos-v1
+          key: llvm-source-17-${{ matrix.os }}-v1
           path: |
             llvm-project/clang/lib/Headers
             llvm-project/clang/include
@@ -58,7 +68,7 @@ jobs:
         uses: actions/cache/restore@v3
         id: cache-llvm-build
         with:
-          key: llvm-build-17-macos-v1
+          key: llvm-build-17-${{ matrix.os }}-v1
           path: llvm-build
       - name: Build LLVM
         if: steps.cache-llvm-build.outputs.cache-hit != 'true'
@@ -82,7 +92,7 @@ jobs:
         uses: actions/cache@v3
         id: cache-wasi-libc
         with:
-          key: wasi-libc-sysroot-v5
+          key: wasi-libc-sysroot-${{ matrix.os }}-v1
           path: lib/wasi-libc/sysroot
       - name: Build wasi-libc
         if: steps.cache-wasi-libc.outputs.cache-hit != 'true'
@@ -98,7 +108,7 @@ jobs:
         run: make tinygo-test
       - name: Make release artifact
         shell: bash
-        run: cp -p build/release.tar.gz build/tinygo.darwin-amd64.tar.gz 
+        run: cp -p build/release.tar.gz build/tinygo.darwin-${{ matrix.goarch }}.tar.gz
       - name: Publish release artifact
         # Note: this release artifact is double-zipped, see:
         # https://github.com/actions/upload-artifact/issues/39
@@ -108,8 +118,8 @@ jobs:
         # We're doing the former here, to keep artifact uploads fast.
         uses: actions/upload-artifact@v3
         with:
-          name: darwin-amd64-double-zipped
+          name: darwin-${{ matrix.goarch }}-double-zipped
-          path: build/tinygo.darwin-amd64.tar.gz
+          path: build/tinygo.darwin-${{ matrix.goarch }}.tar.gz
       - name: Smoke tests
         shell: bash
         run: make smoketest TINYGO=$(PWD)/build/tinygo