Allow symlinks only for the rust-dev tarball

Author: nikic

src/bootstrap/src/core/build_steps/dist.rs

@@ -2224,6 +2224,8 @@ impl Step for RustDev {
 
         let mut tarball = Tarball::new(builder, "rust-dev", &target.triple);
         tarball.set_overlay(OverlayKind::LLVM);
+        // LLVM requires a shared object symlink to exist on some platforms.
+        tarball.permit_symlinks(true);
 
         builder.ensure(crate::core::build_steps::llvm::Llvm { target });