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

[Joshua Cranmer via cfe-commits]

jcranmer-intel wrote:

> (Sidenote: "dynamic" isn't even [documented](https://clang.llvm.org/docs/UsersManual.html#cmdoption-fdenormal-fp-math)).

It's not a selectable enum of the Clang `-fdenormal-fp-math` flag, but it is one for the LLVM function attribute `denormal-fp-math`.

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