fix not defined var

Author: Jason2866

builder/frameworks/arduino.py

@@ -34,7 +34,8 @@
 SConscript("_embed_files.py", exports="env")
 
 if "espidf" not in env.subst("$PIOFRAMEWORK"):
-    if os.path.exists(join(FRAMEWORK_DIR, "tools", "platformio-build.py")):
+    if os.path.exists(join(DefaultEnvironment().PioPlatform().get_package_dir(
+            "framework-arduinoespressif32"), "tools", "platformio-build.py")):
         PIO_BUILD = "platformio-build.py"
     else:
         PIO_BUILD = "pioarduino-build.py"