[llvm] SimplifyLibCalls: Don't require ldexp to emit intrinsic in exp2 combine (PR #92707)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> It looks like the lowering for llvm.ldexp currently doesn't respect "no-builtin-ldexp" etc.; we should probably fix that first.
> 

When I tried to consider no-builtin* for expanding memcpy instead of emitting a call, I got complaints (and had to implement c8cac156135de8e211b800ea5abe9666803b2875) because for some reason there was the expectation of this not changing legalization emitted libcalls. We have parallel tables, TargetLibraryInfo and RuntimeLibcalls, and it's not clear if no-builtin is supposed to change the RuntimeLibcall behavior 

https://github.com/llvm/llvm-project/pull/92707