manually apply babel in older ember-cli versions

lib/ember-addon-main.js

@@ -96,13 +96,36 @@ module.exports = {
         }
 
         this._addon.logger.debug(`setup *.hbs compiler with ${htmlbarsOptions.pluginNames}`);
-        return debugTree(
+        let output = debugTree(
           this._addon.transpileTree(inputTree, {
             isProduction,
             ...htmlbarsOptions,
           }),
           '03-output'
         );
+
+        let checker = new VersionChecker(this._addon.project).for('ember-cli', 'npm');
+        let requiresBabelTree = checker.lt('3.13.0');
+        let isAddon = this._addon.parent !== this._addon.project;
+
+        // as a result of https://github.com/ember-cli/ember-cli-htmlbars/pull/749 we are relying
+        // on babel for all template comilation. This works fine since ember-cli@3.13 but before
+        // that there was a different path for **addon** templates and they would not be compiled
+        // correctly. This change wraps the output of addons in a babel tree since ember-cli
+        // isn't doing that properly.
+        if (requiresBabelTree && isAddon) {
+          let babelAddon = this._addon.parent.addons.find(
+            (addon) => addon.name === 'ember-cli-babel'
+          );
+          output = babelAddon.transpileTree(output, {
+            babel: this._addon.parent.options.babel,
+            'ember-cli-babel': {
+              compileModules: false,
+            },
+          });
+        }
+
+        return output;
       },
 
       precompile(string, _options) {