In the test from https://reviews.llvm.org/D7098, `char array[len];` is
32-byte aligned on most targets whether it is instrumented or not
(optimized by StackSafetyAnalysis), due to the the used `*FrameLowering`
being `StackRealignable`.
However, when using `SystemZELFFrameLowering`, an un-instrumented
`char array[len];` is only 8-byte aligned.
Ensure `char array[len];` gets instrumented like what we did to
`alloca_vla_interact.cpp`, to make the test pass on s390x.
ebd4dc4263