Fix CI.
a) Update canonical binaries.
b) Fix an out-of-bounds access in `clear-stream`. This also required supporting
a new instruction in `subx run` to load an imm8 into rm8.
Fix a major discrepancy between the SubX VM and real x86 processors. This
was responsible for the breakage identified in commit 4684. We now have
failing tests, but at least they are identical running natively and on
SubX.
Kartik Agaram