add EMCC_JSOPT_BLACKLIST env var; fixes #2819

emcc

@@ -1346,8 +1346,12 @@ try:
   js_optimizer_queue = []
   js_optimizer_extra_info = {}
   js_optimizer_queue_history = []
+  js_optimizer_blacklist = (os.environ.get('EMCC_JSOPT_BLACKLIST') or '').split(',')
   def flush_js_optimizer_queue():
     global final, js_optimizer_queue, js_optimizer_extra_info, js_optimizer_queue_history
+
+    js_optimizer_queue = filter(lambda p: p not in js_optimizer_blacklist, js_optimizer_queue)
+
     if len(js_optimizer_extra_info) == 0:
       js_optimizer_extra_info = None
     if len(js_optimizer_queue) > 0 and not(not shared.Settings.ASM_JS and len(js_optimizer_queue) == 1 and js_optimizer_queue[0] == 'last'):