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

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

> It's reasonable to turn this on because we are targeting SPIR-V for AMD machines and want coverage, but it's not reasonable to make this the solution for failing tests.

Agreed. We also still have bots that do *not* turn on this target.

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