[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

Author: daltenty

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)?;

src/bootstrap/src/core/build_steps/compile.rs

@@ -330,7 +330,7 @@ fn copy_third_party_objects(
 
     if target == "x86_64-fortanix-unknown-sgx"
         || builder.config.llvm_libunwind(target) == LlvmLibunwind::InTree
-            && (target.contains("linux") || target.contains("fuchsia"))
+            && (target.contains("linux") || target.contains("fuchsia") || target.contains("aix"))
     {
         let libunwind_path =
             copy_llvm_libunwind(builder, target, &builder.sysroot_target_libdir(*compiler, target));