SI-8845 Control flow pot-pourri crashes GenASM, but not -BCode

Given that we'll switch to GenBCode in 2.12, the test case
showing the bug is fixed under that option is all I plan to
offer for this bug.

The flags file contains `-Ynooptimize` to stay locked into
`GenBCode`.
Merge pull request #3982 from retronym/ticket/8845

SI-8845 Control flow pot-pourri crashes GenASM, but not -BCode