rustbuild: include llvm-libunwind in dist tarball
rustbuild: include llvm-libunwind in dist tarball

Signed-off-by: Marc-Antoine Perennou <07f76cf0511c79b361712839686f3cee8c75791c@Perennou.com>

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust