Make SIMD checker tests more robust.

Rationale:
With more and more peeling and cleanup loops coming up,
some of our checker tests were a bit fragile testing for
the first Phi occurrence. This CL fixes that. Also fixes
a few omissions found during the refactoring.

Test: test-art-host test-art-target
Change-Id: I9b27237cf048981ca2b5a18057e09211b7002486