[AIX] handle libunwind native_libs

AIX should follow a similar path here to other libunwind platforms, with regards to system vs in-tree libunwind and the native lib search directories

compiler/rustc_metadata/src/native_libs.rs

@@ -57,6 +57,7 @@ pub fn walk_native_lib_search_dirs<R>(
     if sess.target.vendor == "fortanix"
         || sess.target.os == "linux"
         || sess.target.os == "fuchsia"
+        || sess.target.is_like_aix
         || sess.target.is_like_osx && !sess.opts.unstable_opts.sanitizer.is_empty()
     {
         f(&sess.target_tlib_path.dir, false)?;