treat int 0x2d as a direct or indirect branch for cases where it does not raise an exception but directly transfers control

Xref #2126: when int 2d raises EXCEPTION_BREAKPOINT, we have to deal with ExceptionAddress different from CONTEXT.Eip.

int 2d has other behavior: sometimes it doesn't raise an exception and simply functions as a branch. This issue covers that case. Xref the discussion in https://github.com/DynamoRIO/dynamorio/pull/2218 from which I'm quoting here:

If I build 64-bit, instead of 8 EXCEPTION_BREAKPOINTs (i.e., an exception for every single int 2d) I only get 4 -- so is it that for 32-bit, an exception is raised every time on int 2d, but for 64-bit it varies based on eax?

It seems like we have to treat int 2d as a control transfer instruction for 64-bit. So you have the rules for exactly where it goes? Is it based only on eax? So if we can find the eax statically we can treat it as a direct
branch, but if the eax set is not visible in the current block we may have to treat it as an indirect branch.