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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> I may have mentioned a few times that I don't like function attributes controlling fast-math behaviors.

It doesn't control it, it's informative. You just get undefined behavior if you end up calling mismatched mode functions.

It does control it in the AMDGPU entry point function case, since we are more or less directly programming the initial register state on kernel launch in the compiler 

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