Windows compatibility

[rspeir]

Hi krzmaz,

I converted the perl script that generates the fsdata.c into a python script that doesn't rely on *nix shell commands. I also modified the cmakelists file slightly so that it uses the new python script and doesn't rely on the *nix mv command to rename the generated fsdata.c file to my_fsdata.c.

The project will build under Windows now, and I tested it on an Ubuntu install to verify it still works under Linux. I don't have a MacOS install to test it on, but I don't see why it wouldn't work.

Please excuse the ugliness of my python script; it's probably not the most "pythonic" way of doing things, as I was just doing a dirty line-by-line conversion of the perl script your project pulled in.

[rspeir]

Hi krzmaz,

It's my turn to apologize for the long delay. I got super busy with work and had a bout with Covid. I have read your comments and made a few modifications to the cmakelists file that I think offer a good compromise:

1. As stated above, its use is not limited to this repository, it could be an external dependency like the original `makefsdata` script.
2. Its maintenance/further development should be separate from the version history of this repository

I have separated my python script into its own gist on my github page.

3. I think we should extend the Perl script, rather than reinventing it. AFAIK Python3 is also not installed on Windows by default. Therefore I see no difference in depending on having Python3 interpreter over depending on an Perl interpreter. Especially that according to https://www.perl.org/get.html, Perl is installed by default on 2 out of 3 major platforms, whereas AFAIK it is not a given for Python3 to be present on every linux distro.

I installed a perl interpreter on my PC to see if the script would work without modification in a Windows environment, but it still utilizes certain shell commands that work differently on Windows than a *nix environment, so even with a perl interpreter installed, it won't work under Windows.

You are correct that Python 3 is not installed by default on Windows, but many of the installation scripts that install the Raspberry Pi Pico dev tools also install it, so I thought it would be more likely that someone using this repo would also have Python 3.

Modifying the original perl script is probably the "cleanest" option, but I have never particularly liked the language and don't know enough about it to make changes to the script.

Steps that I would propose:

* create another PR for the original Perl script to make it Windows friendly (preferably on top of [my PR](https://github.com/lwip-tcpip/lwip/pull/15))

* extract your Python script to a more generally available location as suggested above

* add logic in CMake to:
  
  1. Check for Perl and if it is available, use the original `makefsdata` script (the forked version until the PR gets merged)
  2. If Perl isn't available, check for Python3, and if it is available print a warning about it and fall back to your external Python script
  3. If both Perl and Python3 aren't available print a fatal error suggesting to install Perl

Here's my solution:

1. Check what OS cmake is running under
2. If it's running under Windows (and the original perl script won't work at all) then pull in the python version of makefsdata
3. If it's not running under Windows, default to using the perl version of the script.

[krzmaz]

@rspeir sounds good, can you rebase your changes accordingly?