Cygwin: enable arm nuttx upload within cygwin

In the Cygwin environment the native Windows serial COM# ports get mapped
to /dev/ttyS# for POSIX compatibility. While # is one number lower inside
the environment than the COM port number because it's 0 indexed instead
of 1.

I added the necessary handling to all the dependent parts I found which
allows uploading to /dev/ttyS# when the cygwin platform is detected.
Now the usual "make px4fmu-v4 upload" and
"./Tools/upload.sh build/px4fmu-v4_default/px4fmu-v4_default.px4" work.

Tools/px_uploader.py

@@ -667,7 +667,7 @@ def main():
             # on unix-like platforms use glob to support wildcard ports. This allows
             # the use of /dev/serial/by-id/usb-3D_Robotics on Linux, which prevents the upload from
             # causing modem hangups etc
-            if "linux" in _platform or "darwin" in _platform:
+            if "linux" in _platform or "darwin" in _platform or "cygwin" in _platform:
                 import glob
                 for pattern in patterns:
                     portlist += glob.glob(pattern)
@@ -690,6 +690,10 @@ def main():
                         # OS X, don't open Windows and Linux ports
                         if "COM" not in port and "ACM" not in port:
                             up = uploader(port, args.baud_bootloader, baud_flightstack)
+                    elif "cygwin" in _platform:
+                        # Cygwin, don't open native Windows COM and Linux ports
+                        if "COM" not in port and "ACM" not in port:
+                            up = uploader(port, args.baud_bootloader, baud_flightstack)
                     elif "win" in _platform:
                         # Windows, don't open POSIX ports
                         if "/" not in port: