BPF: add a test for selectiondag alias analysis w.r.t. lifetime

BPF: add a test for selectiondag alias analysis w.r.t. lifetime

This adds a test for the bug
  https://bugs.llvm.org/show_bug.cgi?id=47591

Previously, selection dag has a bug which may incorrectly
assume no alias when crossing a lifetime boundary and this
may generate incorrect code as demonstrated in the above bug.

It looks the bug is fixed by https://reviews.llvm.org/D91833.
Basically, when comparing two potential memory access dag nodes,
  a store and a lifetime.start,
with the same frame index.
Previously, it may be decided no alias. With the above fix,
these two will be considered aliasing which will prevent
incorrect code scheduling.

Differential Revision: https://reviews.llvm.org/D92451