[HTML5] Scons now expects "emcc" to be in PATH.

No longer parse emscripten/emsdk config to detect emcc/node paths.
Use WhereIs to find "emcc" and "node", look for "node_modules" in "emcc"
path.

(cherry picked from commit 7998745237)

platform/javascript/detect.py

@@ -1,6 +1,7 @@
 import os
 
-from emscripten_helpers import parse_config, run_closure_compiler, create_engine_file
+from emscripten_helpers import run_closure_compiler, create_engine_file
+from SCons.Util import WhereIs
 
 
 def is_active():
@@ -12,7 +13,7 @@ def get_name():
 
 
 def can_build():
-    return "EM_CONFIG" in os.environ or os.path.exists(os.path.expanduser("~/.emscripten"))
+    return WhereIs("emcc") is not None
 
 
 def get_opts():
@@ -100,9 +101,6 @@ def configure(env):
     # Closure compiler extern and support for ecmascript specs (const, let, etc).
     env["ENV"]["EMCC_CLOSURE_ARGS"] = "--language_in ECMASCRIPT6"
 
-    em_config = parse_config()
-    env.PrependENVPath("PATH", em_config["EMCC_ROOT"])
-
     env["CC"] = "emcc"
     env["CXX"] = "em++"
     env["LINK"] = "emcc"