[jitlink][rtdyld][checker] Re-apply 4b17c81d with fixes.

This re-applies 4b17c81d, "[jitlink/rtdydl][checker] Add TargetFlag
dependent disassembler switching support", which was reverted in
4871a9ca due to bot failures.

The patch has been updated to add missing plumbing for Subtarget Features and
a CPU string, which should fix the failing tests.

https://reviews.llvm.org/D158280