[llvm] [Support] Modernize PointerLikeTypeTraits with llvm::is_detected (NFC) (PR #157021)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

Closing.

This is failing on Windows due to the way I handle the pointer of an incomplete type - `Incomplete *`.   I could fix this, but that doesn't really result in simplification or line count reduction.

https://github.com/llvm/llvm-project/pull/157021