[libclc] [libclc] Use custom CMake handling to overhaul libclc compilation (PR #185247)

[Konrad Kleine via cfe-commits]

kwk wrote:

@arsenm I'll take a look at c5cb48c. Thank you.

> > Also I think there used to be more files than libclc.bc, right?
> 
> I don't think so (though I am moving towards having there be more artifacts)

Please take a look at the last expandable line my former comment to see a list which includes files like these here:

```
/usr/lib64/clc/amdgcn--amdhsa.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
/usr/lib64/clc/aruba-r600--.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
/usr/lib64/clc/barts-r600--.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
/usr/lib64/clc/bonaire-amdgcn--.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
/usr/lib64/clc/bonaire-amdgcn-mesa-mesa3d.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
/usr/lib64/clc/caicos-r600--.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
/usr/lib64/clc/carrizo-amdgcn--.bc                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
/usr/lib64/clc/carrizo-amdgcn-mesa-mesa3d.bc   
```

That's what I meant by "more files".

https://github.com/llvm/llvm-project/pull/185247