Implement single-stepping (int 1 upon TF = 1)

[tkchia]

[ghaerr]

Ditto my comment on https://github.com/jart/blink/pull/135#issuecomment-1552148471.

[tkchia]

Hello @ghaerr,

Looks like the tests passed when I retried them. :raised_eyebrow:

[ghaerr]

That's great @tkchia. Now if we could just figure out why they're inconsistently failing... and I'm still wondering about popcnt, since it failed on me twice without any changes to the VM!

[tkchia]

Hello @jart,

I would like your feedback on this PR, as it is somewhat intrusive and impinges on the underlying workings of Blink's JITter.

My general goal is to keep the common case — x86-64 guest code running with JIT enabled, and without single-stepping — as fast as before.

Thank you!

[jart]

I'll take a look into this in a week when I'll have time to give this the attention it needs.