[llvm-branch-commits] [lld] Make cache-warning* tests work with internal shell (PR #156537)

[Fangrui Song via llvm-branch-commits]

https://github.com/MaskRay approved this pull request.

LGTM.

It's good to get rid of `$(($(cat %t.size.txt) + 5))`

https://github.com/llvm/llvm-project/pull/156537