Add lldb smoke test (#1241)

* add lldb runner

* don't build wasmtime

* use brew's lldb

* disable for macos

* set LLDB on linux

* re-org gh actions and cfg

* address feedback

.github/actions/define-llvm-env/main.js

@@ -0,0 +1,13 @@
+#!/usr/bin/env node
+
+// On OSX pointing to brew's LLVM location.
+if (process.platform == 'darwin') {
+  console.log("::set-env name=DWARFDUMP::/usr/local/opt/llvm/bin/llvm-dwarfdump");
+  console.log("::set-env name=LLDB::/usr/local/opt/llvm/bin/lldb");
+}
+
+// On Linux pointing to specific version
+if (process.platform == 'linux') {
+  console.log("::set-env name=DWARFDUMP::/usr/bin/llvm-dwarfdump-9");
+  console.log("::set-env name=LLDB::/usr/bin/lldb-9");
+}