My understanding of the problem is that there are three cases for linking LLVM: static bundled copy, static system copy, and dynamic system copy. The first is easy to handle because it's decided by the configure script so we know when we're in that case and can do whatever we need to, so the only difficulty is handling the two system library cases.
The current solution involves using
#[link(..., kind = "static")] for static libraries and
#[link(..., kind = "dylib")] (or usually leaving it off because it's the default) for dynamic ones, which is hard because
pkg-config and similar tools don't tell you whether the library you're linking against is static or dynamic. The reason they don't tell you is because in the C world you basically don't care: in either case you just pass
-lfoo when running the linker (there are edge cases that don't work, but those don't work with Rust's method either). As far as I can tell there's nothing preventing Rust from doing the same thing.
That behavior is what
kind = "dylib" produces.
kind = "static" searches the system for the archive file, unpacks it, and then bundles all the objects into the resulting rlib (or whatever you're producing). This is useful if the archive is some bundled library that you don't want to install separately (like the bundled LLVM case), but it's a weird thing to do with a system library. Just using the "dylib" behavior for any system library should just work because it matches the C behavior that linking was built up around.
(As a disclaimer I can only comment from a Linux point of view. As I understand it things are more complicated in Windows. There are some more details and discussion of this whole thing (including some Windows stuff) in a previous internals thread.)