byval parameter should have align 8 on aix

compiler/rustc_target/src/callconv/powerpc64.rs

@@ -58,8 +58,10 @@ where
 
     // The AIX ABI expect byval for aggregates
     // See https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/Targets/PPC.cpp.
+    // The incoming parameter is represented as a pointer in the IR,
+    // the alignment is associated with the size of the register. (align 8 for 64bit)
     if !is_ret && abi == AIX {
-        arg.pass_by_stack_offset(None);
+        arg.pass_by_stack_offset(Some(Align::from_bytes(8).unwrap()));
         return;
     }