[lld] [lld][test] Fix file cleanup in aarch64-build-attributes.s (PR #164396)

[Cullen Rhodes via llvm-commits]

https://github.com/c-rhodes approved this pull request.

i think the new layout is more sensible, so LGTM

the output of tree on the new layout in the description looks wrong tho, was this done manually? The .o files dont seem to be under the tmp directory`aarch64-build-attributes.s.tmp`, like the .s files in the original layout

https://github.com/llvm/llvm-project/pull/164396