ci: add check that TinyGo can be built using Homebrew LLVM

This is supposed to work, but there was no CI check. Add it to make sure
it continues to work.

.github/workflows/build-macos.yml

@@ -100,3 +100,28 @@ jobs:
       - name: Smoke tests
         shell: bash
         run: make smoketest TINYGO=$(PWD)/build/tinygo AVR=0
+  test-macos-homebrew:
+    name: homebrew-install
+    runs-on: macos-latest
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: '1.18'
+      - name: Install LLVM
+        shell: bash
+        run: |
+          HOMEBREW_NO_AUTO_UPDATE=1 brew install llvm@14
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Cache Go
+        uses: actions/cache@v2
+        with:
+          key: go-cache-macos-homebrew-v1-${{ hashFiles('go.mod') }}
+          path: |
+            ~/Library/Caches/go-build
+            ~/go/pkg/mod
+      - name: Build TinyGo
+        run: go install
+      - name: Check binary
+        run: tinygo version