[OpenMP] Remove the new runtime default for AMDGPU

The new runtime is currently broken for AMD offloading. This patch makes
the default the old runtime only for the AMD target.

Reviewed By: ronlieb

Differential Revision: https://reviews.llvm.org/D114965

GitOrigin-RevId: 96ff74a0d5982cb70ac25883f3b0d5bb99947aa9
3 files changed