orccompiler: Allow fallback to backup/emulation if the target specific register allocation fails
orccompiler: Allow fallback to backup/emulation if the target specific register allocation fails

The OrcCode of the program wouldn't be filled with all required fields
if the register allocation happens to early.

okuoku/nmosh-orc,ijsf/OpenWebRTC-orc,mojaves/orc,mojaves/orc,jpakkane/orc,jpakkane/orc,ijsf/OpenWebRTC-orc,jpakkane/orc,Distrotech/orc,okuoku/nmosh-orc,MOXfiles/orc,okuoku/nmosh-orc,MOXfiles/orc,MOXfiles/orc,Distrotech/orc,Distrotech/orc,ijsf/OpenWebRTC-orc,mojaves/orc