MacOS: runtime feature or DYLD_LIBRARY_PATH

[jedbrown]

When running on GH Actions macos-14 (aka. macos-latest), there are two ways to use the libclang provided by brew install llvm@19.

1. Enable the runtime feature.
2. export DYLD_LIBRARY_PATH=$(/opt/homebrew/opt/llvm@19/bin/llvm-config --libdir) without the runtime feature

When using bindgen from build.rs, which is going to give users a better experience?

Note that there have been issues (such as twistedfall/opencv-rust#462 (comment)) when the runtime feature is used inconsistently between crates. On Linux and Windows (using libclang from apt and chocolatey respectively), we have found that the runtime feature is unnecessary and harmless.

This comes back to how clang-sys handles linking, but I think bindgen should make a clear a recommendation about this feature.