[llvm] [NFC] Remove redundant `sys/file.h` header. (PR #124684)

[Nick Desaulniers via llvm-commits]

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

Let's try this, but if merging it breaks the build, let's revert? Consider mentioning https://github.com/llvm/llvm-project/commit/536736995bf5d073853c7e884968c9847b4ae64d in the commit message when you merge this.  Thanks for the patch!

https://github.com/llvm/llvm-project/pull/124684