Detect javascript platform using EMSCRIPTEN env as well

(cherry picked from commit 33daf4d8bc17f30c85cefe2e9dfe9b46ddb257f9)

platform/javascript/detect.py

@@ -12,7 +12,8 @@ def get_name():
 
 
 def can_build():
-    return ("EMSCRIPTEN_ROOT" in os.environ)
+
+    return ("EMSCRIPTEN_ROOT" in os.environ or "EMSCRIPTEN" in os.environ)
 
 
 def get_opts():
@@ -39,7 +40,11 @@ def configure(env):
 
     env.Append(CPPPATH=['#platform/javascript'])
 
-    em_path = os.environ["EMSCRIPTEN_ROOT"]
+    env['ENV'] = os.environ
+    if ("EMSCRIPTEN_ROOT" in os.environ):
+        em_path = os.environ["EMSCRIPTEN_ROOT"]
+    elif ("EMSCRIPTEN" in os.environ):
+        em_path = os.environ["EMSCRIPTEN"]
 
     env['ENV']['PATH'] = em_path + ":" + env['ENV']['PATH']