Use `-text` git attribute instead of `text eol=...`

These automatic conversions lead to issues in various workflows, and all
we want here are files that retain their line endings under all
circumstances. `-text` captures that perfectly well and leads to fewer
issues.

It is preferable to `binary`, because with `-text` we still get textual
diffs.

Differential Revision: https://reviews.llvm.org/D124606