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

[Matt Arsenault via cfe-commits]

arsenm 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

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