Retrieve framework list in a safer way

Resolve #551

Author: valeros

builder/main.py

@@ -105,7 +105,8 @@ def BeforeUpload(target, source, env):  # pylint: disable=W0613,W0621
 # Target: Build executable and linkable firmware
 #
 
-if "zephyr" in env.get("PIOFRAMEWORK", []):
+frameworks = env.get("PIOFRAMEWORK", [])
+if "zephyr" in frameworks:
     env.SConscript(
         join(platform.get_package_dir(
             "framework-zephyr"), "scripts", "platformio", "platformio-build-pre.py"),
@@ -219,7 +220,7 @@ def _jlink_cmd_script(env, source):
 
     upload_actions = [env.VerboseAction("$UPLOADCMD", "Uploading $SOURCE")]
 
-    if "arduino" in env.get("PIOFRAMEWORK"):
+    if "arduino" in frameworks:
         if env.subst("$BOARD").startswith("portenta"):
             upload_actions.insert(
                 0,