Add warning message for MSYS users

qmk_cli/script_qmk.py

@@ -9,6 +9,7 @@ import subprocess
 import sys
 from functools import lru_cache
 from pathlib import Path
+import platform
 
 import milc
 
@@ -69,6 +70,11 @@ def main():
         print('Warning: Your Python version is out of date! Some subcommands may not work!')
         print('Please upgrade to Python 3.6 or later.')
 
+    if 'windows' in platform.platform().lower():
+        if 'mingw64' not in sys.executable or 'mingw64' not in os.environ.get('MSYSTEM_PREFIX', ''):
+            print('Warning: It seems you are not using the MINGW64 terminal.')
+            print('While the MSYS one can work, too, we recommend/support you start "MSYS2 MinGW 64-bit".\n')
+
     # Environment setup
     import qmk_cli
     milc.cli.version = qmk_cli.__version__