Rollup merge of #61829 - Keruspe:libunwind-src, r=alexcrichton
Rollup merge of #61829 - Keruspe:libunwind-src, r=alexcrichton

rustbuild: include llvm-libunwind in dist tarball

Without this we cannot build with llvm-libunwind enabled from a release tarball.

Could it be backported in a beta rollup somehow so that this gets fixed before 1.36 is released?

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