Rollup merge of rust-lang#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?

src/bootstrap/dist.rs

@@ -804,6 +804,7 @@ fn copy_src_dirs(builder: &Builder<'_>, src_dirs: &[&str], exclude_dirs: &[&str]
 
         const LLVM_PROJECTS: &[&str] = &[
             "llvm-project/clang", "llvm-project\\clang",
+            "llvm-project/libunwind", "llvm-project\\libunwind",
             "llvm-project/lld", "llvm-project\\lld",
             "llvm-project/lldb", "llvm-project\\lldb",
             "llvm-project/llvm", "llvm-project\\llvm",