[clang] [llvm] [CMake] Move check for dlfcn.h and dladdr to clang (PR #76163)

[Nico Weber via cfe-commits]

nico wrote:

Can you say what motivated this? Change looks fine, but it looks like it fixes a problem someone reported somewhere but this doesn't say what the problem says.

https://github.com/llvm/llvm-project/pull/76163