[clang] [Driver] Introduce ffp-model=aggressive (PR #100453)

[Fangrui Song via cfe-commits]

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

fp-model= => -ffp-model=

LGTM. I expect that the subject explicit mentions -ffp-model=fast behavior difference, even if it becomes less aggressive and unlikely breaks users.

With "Introduce ...", nobody would expect behavior differences.

https://github.com/llvm/llvm-project/pull/100453