Rollup merge of #135966 - mustartt:fix-ppc-abi-test, r=workingjubilee

[AIX] Allow different sized load and store in `tests/assembly/powerpc64-struct-abi.rs`

Sometimes in the llvm backend generates 2 different copy assembly sequence.

1. `lxvd2x` followed immediately by `stxvd2x` (Load VSX Vector 2 Dword, Store VSX Vector 2 Dword) is semantically equivalent to;
2. `lxvw4x` followed immediately by `stxvw4x` (Load VSX Vector 4 Word, Store VSX Vector 4 Word)

Author: matthiaskrgr