[llvm] [Offload][AMDGPU] Enable SPIRV target in build conf (PR #129323)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

In case this is OK, I'll land this on the weekend to see how much damage (if any) it does to our buildbots while not disrupting too many people.

https://github.com/llvm/llvm-project/pull/129323