Fix #168: Use positive forms for conditional jmp.
When disassembling conditional jmp instructions, prefer to use the
non-negated forms of the condition. That is, print :ae
instead
:nb
; :a
for :nbe
; :ge
for :nl
; and :g
for :nle
.
Use the bootstrap file "boot-2021-07-2" when building.
Updated build.sh to select the 21d directory instead of 21c.