[macOS] move llvm to toolset (#4457)

images/macos/tests/LLVM.Tests.ps1

@@ -0,0 +1,9 @@
+$os = Get-OSVersion
+
+Describe "Clang/LLVM" -Skip:($os.IsMonterey) {
+    It "Clang/LLVM is installed and version is correct" {
+        $toolsetVersion = Get-ToolsetValue 'llvm.version'
+        $clangVersion = & "$(brew --prefix llvm)/bin/clang" --version
+        $clangVersion[0] | Should -BeLike "*${toolsetVersion}*"
+    }
+}