all: add initial LLVM 17 support

This allows us to test and use LLVM 17, now that it is available in
Homebrew.

Full support for LLVM 17 (including using it by default) will have to
wait until Espressif rebases their Xtensa fork of LLVM.

.github/workflows/build-macos.yml

@@ -116,11 +116,15 @@ jobs:
   test-macos-homebrew:
     name: homebrew-install
     runs-on: macos-latest
+    strategy:
+      matrix:
+        version: [16, 17]
     steps:
+      - name: Update Homebrew
+        run: brew update
       - name: Install LLVM
-        shell: bash
         run: |
-          HOMEBREW_NO_AUTO_UPDATE=1 brew install llvm@16
+          HOMEBREW_NO_AUTO_UPDATE=1 brew install llvm@${{ matrix.version }}
       - name: Checkout
         uses: actions/checkout@v3
       - name: Install Go
@@ -128,7 +132,13 @@ jobs:
         with:
           go-version: '1.21'
           cache: true
-      - name: Build TinyGo
-        run: go install
+      - name: Build TinyGo (LLVM ${{ matrix.version }})
+        run: go install -tags=llvm${{ matrix.version }}
       - name: Check binary
         run: tinygo version
+      - name: Build TinyGo (default LLVM)
+        if: matrix.version == 16
+        run: go install
+      - name: Check binary
+        if: matrix.version == 16
+        run: tinygo version