[libomptarget] Build DeviceRTL for amdgpu

Passes same tests as the current deviceRTL. Includes cmake change from D111987.
CI is showing a different set of pass/fails to local, committing this
without the tests enabled by default while debugging that difference.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D112227

GitOrigin-RevId: 4d50803ce49ce6b57c4865361c9ba0ad7063b7be
20 files changed