Enable compiling mjsunit tests as ES6 modules

test/mjsunit/testcfg.py

Index: test/mjsunit/testcfg.py
diff --git a/test/mjsunit/testcfg.py b/test/mjsunit/testcfg.py
index 181c8478fed289ffb6ea195279947c296a5374f3..8389696f49fabf7089035ef1c9b4c5304963be79 100644
--- a/test/mjsunit/testcfg.py
+++ b/test/mjsunit/testcfg.py
@@ -34,6 +34,7 @@ from testrunner.objects import testcase
 FLAGS_PATTERN = re.compile(r"//\s+Flags:(.*)")
 FILES_PATTERN = re.compile(r"//\s+Files:(.*)")
 SELF_SCRIPT_PATTERN = re.compile(r"//\s+Env: TEST_FILE_NAME")
+MODULE_PATTERN = re.compile(r"^// MODULE$", flags=re.MULTILINE)
 
 
 class MjsunitTestSuite(testsuite.TestSuite):
@@ -80,6 +81,9 @@ class MjsunitTestSuite(testsuite.TestSuite):
 
     if not context.no_harness:
       files.append(os.path.join(self.root, "mjsunit.js"))
+
+    if MODULE_PATTERN.search(source):
+      files.append("--module")
     files.append(testfilename)
 
     flags += files