[clang] Disable FTZ/DAZ when compiling shared libraries by default. (PR #80475)

[James Y Knight via cfe-commits]

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

One final nit before you submit, though: please update the PR description and the release notes to also mention that x86 no longer modifies `-fdenormal-fp-math` based on `-ffast-math`.

https://github.com/llvm/llvm-project/pull/80475