[compiler-rt] [compiler-rt] Initial support for builtins on GPU targets (PR #95304)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> > It's true for now at least, so we get the `.bc`. I'd love to have an actual object build though, since it would let us resolve things if we ever want the backend to be able to use these.
> 
> Nothing is stopping you from building and using the object today. We just aren't going to guarantee a stable ABI for it now

Potentially we could put the subarchitecture in the triple (I think Arm and DXIL do this) and then build these builtins multiple times. Unfortunately this would take a stupidly long time to configure, since `compiler-rt` already does a million of these `cxx_compiler_has` checks, which take several seconds, so if we start building for 40+ architectures it's going to be very, very slow.

https://github.com/llvm/llvm-project/pull/95304