Add clang-11 for Linux; blank out threading_example on darwin

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     steps:
       - uses: actions/checkout@v1
       - name: Download LLVM
-        run: sudo apt-get install llvm-11
+        run: sudo apt-get install llvm-11 clang-11
       - name: build odin
         run: make release
       - name: Odin run

examples/demo/demo.odin

@@ -1109,6 +1109,11 @@ prefix_table := [?]string{
 };
 
 threading_example :: proc() {
+	if ODIN_OS == "darwin" {
+		// TODO: Fix threads on darwin/macOS
+		return;
+	}
+
 	fmt.println("\n# threading_example");
 
 	{ // Basic Threads