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

Given that the issue exists is old (2.10) and we move to the new
backend in 2.12, I don't plan to fix it 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.
`-Ynooptimise` is required, because the nightly build runs under `-optimise`, which forces the `GenASM` backend to be enabled, see https://github.com/scala/scala/blob/2.11.x/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala#L313. I will change that soon.