Draft: nativeGen/X86: Add UD2 instructions after indirect branches

As noted in the Intel Software Optimization Manual (section 3.4.1.6, Rule 14), the default prediction for indirect branches is to fall-through. This means that the instruction decoder will attempt to decode anything that follows indirect branches. This will inject operations in to the pipeline that are doomed to fail (since our indirect branches will never fallthrough), resulting in resource conflicts.

Fixes #17588.