[llvm] RuntimeLibcalls: Stop opting out of exp10 (PR #148604)

[Alex Rønne Petersen via llvm-commits]

alexrp wrote:

> Except for target specific types (x86_fp80 and ppc_fp128) I think it is preferable if missing FP libcalls that cannot be legalized result in a linker error instead of a compiler error, which allows the user to provide them. At least when considering the world we live in _now_, rather than possible future designs.

I agree with this. A linker error we can straightforwardly address by implementing the missing function in Zig's compiler-rt. An ICE from LLVM is significantly more annoying to work around.

> Is there any real interest in having fp80 work across all x86 targets?

In Zig, we currently lower `f80` to `i80` and manual soft float calls if the target is not x86 with `long double = x86_fp80`. It would be nice if we didn't have to do that, I suppose, but it's not terribly important.

> I expect other languages may get a bit of a surprise though (cc @alexrp for Zig).

I don't believe Zig emits `exp10` intrinsic calls at the moment, FWIW.

https://github.com/llvm/llvm-project/pull/148604