We weren't altering the status flags after a BRK because of the
assumption that a BRK was a crash. For an inline BRK, such as a SOS
call, execution continues. We need to mark NVZC indeterminate or
we may incorrectly handle conditional branches that follow.
The BRK instruction now uses the same flag updater as JSR, since it's
effectively a subroutine call to unknown code. If execution doesn't
continue across the BRK then the flags don't matter.
Updated 20182-extension-scripts to exercise this.
