[msan] Relax origin-alignment test.

[msan] Relax origin-alignment test.

Change origin-alignment test to test only the alignment of the origin
store, and not the exact instruction sequence used to compute the
address. This makes the test less fragile and, in particular, lets it
pass both with the old and new MSan ABIs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254027 91177308-0d34-0410-b5e6-96231b3b80d8