[libclc] [libclc] [cmake] Fix per-target *_convert.cl dependencies (PR #127315)

[Sylvestre Ledru via cfe-commits]

sylvestre wrote:

I will merge it as it as it fixes https://github.com/llvm/llvm-project/issues/127378 and apt.llvm.org has been broken for a few days because of this

This PR can be improved later.


https://github.com/llvm/llvm-project/pull/127315