bootstrap: include llvm-dwp in CI LLVM

This commit includes the `llvm-dwp` tool in the CI LLVM (which rustc
developers can download instead of building LLVM locally) - `llvm-dwp`
is required by Split DWARF which landed in PR rust-lang#77117.

Signed-off-by: David Wood <david@davidtw.co>

src/bootstrap/dist.rs

@@ -2553,6 +2553,7 @@ impl Step for RustDev {
         install_bin("llvm-profdata");
         install_bin("llvm-bcanalyzer");
         install_bin("llvm-cov");
+        install_bin("llvm-dwp");
         builder.install(&builder.llvm_filecheck(target), &dst_bindir, 0o755);
 
         // Copy the include directory as well; needed mostly to build