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

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> > > So, alternatively...we could just go with the simplest solution, and use "ieee" as the default even under -ffast-math.
> 
> +1. **There hasn't been a performance reason to use FTZ/DAZ since ~2011.** Maybe there's still a power benefit? But in that case you could still explicitly request the flush separate from -ffast-math

I don't think this is correct. I know there have been improvements, but there are still cases where setting ftz can have a significant performance impact.

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