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

[Trevor Gross via llvm-commits]

tgross35 wrote:

Actually, is there anything unique about `exp10` here? All `x86_fp80` intrinsics on Apple (as well as Windows) that get lowered to libm calls have the same problem.

> 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.

In theory this could lower to the C23 `exp10f64x` symbol rather than having an error. The long-term correctness of this depends on an assumption that Windows and Apple will either never specify `_Float64x`, or if they do specify it, make it `x86_fp80` (cc https://github.com/llvm/llvm-project/issues/97335).

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