[clang] [llvm] [LLVM][ConstantFP] Replace uses of isExactlyValue(+/-1.0) with isOne/isMinusOne. (PR #204333)

[David Sherwood via cfe-commits]

https://github.com/david-arm approved this pull request.

LGTM! I think this seems reasonable. If there is a clear use case for extending to cover `isTwo`, etc. in future then they can always be added later.

https://github.com/llvm/llvm-project/pull/204333