Uniform handling of undefined aflags

[lkorenc]

After some instructions, value inside some arithmetic flags may be undefined. X86 semantics currently handle this non-uniformly by either using __remill_undefined_* intrinsics, storing arbitrary values, or ignoring the undefined value altogether.

Ideal solution would be to always use __remill_undefined_* but add an extra argument, that can be used to indicate a preferred value.
Unfortunately a list of all affected instructions is rather long. Non-exhaustive list of instructions to check:

• IDIV
• ROR, RCL, ...
• BTS, BTR, BTC, ...