Port ClanBomber to SDL2 on macOS

[RobinNunkesser]

This PR updates ClanBomber to build and run on a modern macOS toolchain by migrating the project from SDL1-era APIs to SDL2 and adjusting the build system for current Homebrew packages.

What changed:

• Replaced SDL1 window, input, threading, and surface APIs with SDL2 equivalents
• Updated Boost usage for modern macOS / Homebrew builds
• Adjusted Autotools detection and generated build files for the new dependency set
• Fixed remaining compile and link issues uncovered during the port

Validation:

• make -j8
• smoke-tested clanbomber2 startup
• verified --fullscreen and --runserver=2 launch paths

[ConnyOnny]

Thanks for having a go at this. I haven't worked on this in 11 years and currently I wouldn't have time for it anyway. So I think I should archive my version of the project and people can come to you for the updated version. What do you think?

[RobinNunkesser]

Thanks for looking into the PR and the fast reply. Archiving the project and perhaps linking to my fork seems to be a good idea, thanks!