Make globalaa-retained.ll test catching more cases.

Summary:
* Add checks for store. That is needed because GlobalsAA is called
  twice in the current pipeline with different sets of Function passes
  following it. However, the loads are eliminated using instcombine
  which happens everywhere. On the other hand, DeadStoreElimination is
  performed only once so by checking for store we'll be able to catch
  more cases when GlobalsAA is invalidated unintentionally.
* Add empty function above/below the test so that we don't depend on
  the relative order of instcombine/dead-store-elimination and the
  pass that invalidates the analysis (inside the same
  FunctionPassManager).

Reviewers: kristof.beyls

Reviewed By: kristof.beyls

Subscribers: llvm-commits, n.bozhenov

Differential Revision: https://reviews.llvm.org/D32015
Patch by Andrei Elovikov <andrei.elovikov@intel.com>

llvm-svn: 300553