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

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> I don't think it's unreasonable to switch the logic of `-mdaz-ftz` from linking a file with a global initializer that sets the flags to making it emit the entry-point call to such a function instead, it still largely follows the same logic to me. And having a command line flag makes it easier for users to access rather than manually linking in a file located who-knows-where in the toolchain (although I suspect anyone who cares hard enough would rather just write the calls to set FTZ/DAZ than track it down from the toolchain).

I suppose there's also some portability value in supporting this gcc option. I guess I'd be OK with it.

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