Merge pull request #1814 from jason-simmons/mojo_toolchain_path

Try to locate the toolchain in the output layout used by the Flutter …

packages/flutter_tools/lib/src/toolchain.dart

@@ -32,6 +32,9 @@ class Compiler {
 Future<String> _getCompilerPath(BuildConfiguration config) async {
   if (config.type != BuildType.prebuilt) {
     String compilerPath = path.join(config.buildDir, 'clang_x64', 'sky_snapshot');
+    if (FileSystemEntity.isFileSync(compilerPath))
+      return compilerPath;
+    compilerPath = path.join(config.buildDir, 'sky_snapshot');
     if (FileSystemEntity.isFileSync(compilerPath))
       return compilerPath;
     return null;