SI-8925, SI-7407 test cases, fixed in new backend

Given that the issues are old (2.10) and we move to the new backend
in 2.12, I don't plan to fix them in GenASM.

The test case for 7407 existed already, this commit just adds
`-Yopt:l:none` to the flags to make no dead code is eliminated.
Merge pull request #4068 from lrytz/t8925

SI-8925, SI-7407 test cases, fixed in new backend