use natural align 4 for byval args

Author: mustartt

compiler/rustc_target/src/callconv/powerpc64.rs

@@ -58,8 +58,9 @@ where
 
     // The AIX ABI expect byval for aggregates
     // See https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/Targets/PPC.cpp.
+    // natural alignment of byval pointer are align 4
     if !is_ret && abi == AIX {
-        arg.pass_by_stack_offset(None);
+        arg.pass_by_stack_offset(Some(Align::from_bytes(4).unwrap()));
         return;
     }