[llvm] [Offload] Do not link every target for JIT (PR #92013)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> But this doesn't work as your expectation because the AMDGPU code is there when you turn the macro on, no matter whether you build it for AMDGPU or NVPTX.
> 
> If you want to do that, one solution would be to add `JIT.cpp` as target source if the target is in support list when you build the corresponding plugin, instead of having it as a common component.

I suppose that's fair. It's easier to just put it there than it is to rework that bit.

https://github.com/llvm/llvm-project/pull/92013