[libomptarget] Run GPU offloading tests on both new and old runtime

Implemented by patching python config instead of modifying all
the tests so that -generic and XFAIL work as usual. Expectation is for
this to be reverted once the old runtime is deleted.

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D112225

GitOrigin-RevId: bf6f955f393f9922ac743ff2055bf867a7a071ae
5 files changed