[llvm] [Support] Refactor getN1Bits so it does not work around any g++ bug (PR #78933)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

@AtariDreams It doesn't appear like this PR (or #87560, #87313, #85162, or #91386) have been approved by a reviewer? The LLVM review policy technically does allow post-commit review, but that is typically de-facto reserved for code owners working in their specific area. These PRs should probably be reverted until they are adequately reviewed.

https://github.com/llvm/llvm-project/pull/78933