Update comment on Large module

Author: winstonallo

tests/assembly-llvm/reg-struct-return.rs

@@ -107,8 +107,7 @@ mod Pivot {
 
 // Verifies ABI changes for a struct of size 12, which is larger than the
 // maximum size for reg-struct-return (8 bytes).
-// Here, both WITH and WITHOUT should use the hidden pointer convention (i.e, they
-// should be identical).
+// Here, the hidden pointer convention should be used even when `-Zreg-struct-return` is set.
 mod Large {
     struct LargeStruct {
         a: i32,