codegen_ssa: use llvm-objcopy for macOS strip

compiler/rustc_codegen_ssa/messages.ftl

@@ -2,6 +2,8 @@ codegen_ssa_L4Bender_exporting_symbols_unimplemented = exporting symbols not imp
 
 codegen_ssa_add_native_library = failed to add native library {$library_path}: {$error}
 
+codegen_ssa_aix_strip_not_used = using host's `strip` binary to cross-compile to AIX which is not guaranteed to work
+
 codegen_ssa_apple_deployment_target_invalid =
     failed to parse deployment target specified in {$env_var}: {$error}