[llvm] [ADT] Simplify SparseBitVectorElement::unionWith and friends. NFC. (PR #143775)

[Jay Foad via llvm-commits]

jayfoad wrote:

No effect on compile time: https://llvm-compile-time-tracker.com/compare.php?from=756e7cfd86c7f2bf20aaa1a3f87b5aa72ec128b4&to=1775d80ec58eeeac8be33498d3ee860ded281e36&stat=instructions:u

https://github.com/llvm/llvm-project/pull/143775