[libclc] [libclc] Move __clc_ldexp to CLC library (PR #126078)

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

> The amdgpu customization should be removed. This is legacy code from before we had the ldexp intrinsic. Regular __builtin_ldexp* should work now

Good to know, thanks. No one else in libclc is using `__builtin_ldexp`, so in its current form it'd still have to be some sort of a customization. Everyone is opting for the software implementation.

We could have `__builtin_ldexp*` in the default implementation, but guard it behind a macro that only AMD defines. Would we ideally have an `__builtin_elementwise_ldexp` to target the vector intrinsics directly?

https://github.com/llvm/llvm-project/pull/126078