Initial changes for LLVM 18 compatibility on macOS

[jonpalmisc]

I've made some minimal changes to get Nyxstone to build with LLVM 18 on macOS:

• Adjusted find_package call to not specify the LLVM version. I think it's probably best to not force a specific LLVM version considering a new major release of LLVM is available roughly every 6 months.
• Removed a similar version check from the Python bindings build script.
• Pruned the results of llvm-config --ldflags, which returns multiple flags on my system, only the first of which is the needed '-L' flag.
• Removed link arguments that are unknown on macOS.

Notable TODOs include:

• Updating Rust bindings build script.
• Probably other stuff?

If these changes look good and support for LLVM 18 is desired, I can go ahead and clean these up and test on other platforms; otherwise, I'll just use my fork for now.

[jonpalmisc]

Another notable TODO I just realized: updating the README.

[stuxnot]

I've merged this branch into #55, so that LLVM 18 will land for c++, rust, and python at the same time. Thank you for your work!