[1.30 beta] Missing LLVM shared library

[pietroalbini]

A crate doesn't work anymore because we stopped shipping LLVM as a shared library.

• rustc-llvm-proxy 0.1.1 regressed from stable to beta (build log) cc @denzp

cc @alexcrichton

[eddyb]

cc @rust-lang/compiler We should be allowed to break code that bypasses toolchain stability, right?
We don't guarantee what we put in the sysroot, or where it is, and these crates should ideally not even allow themselves to be used outside of nightly.

[nagisa]

Similar to #48714. Closing.