Fix Windows build

[mrexodia]

• Automatically fetch SDL2 if it cannot be found
• Use std::numbers::pi instead of non-standard M_PI to fix dummy build
• Use path.string() where needed to fix compilation

[danielzgtg]

I reproduced the .string() problem, thank you for fixing our oversight of tts-server!

I made two minor suggestions for improvement.

[danielzgtg]

@mmwillet Pinging as this will use your CI minutes.

I plan to merge after 24 hours, despite the Windows runner being projected to more than triple the minutes used, because we weren't using many CI minutes to begin with.

[ecyht2]

I do have Windows VMs, I might be able to test it out. @mrexodia, are you using msvc or mingw?

Edit: Whoops probably should read the code first.

[mrexodia]

I am using MSVC. If you want to test you can use a zig toolchain: https://github.com/mrexodia/zig-cross

[ecyht2]

Can you also update the README.md to show that we have Windows support?

[mrexodia]

Can you also update the README.md to show that we have Windows support?

I do not know what to change in the feature matrix because I did not test everything. I think this should be done by one of the maintainers and not a random contributing some minor compilation fixes 😅

[mrexodia]

I also fixed the Linux build, tested locally with Ubuntu 24.04 LTS