[InstCombine] add test for possible zext-phi transform; NFC
[InstCombine] add test for possible zext-phi transform; NFC

The datalayout doesn't include i1, so we don't do a potential shrink and sink transform.

Example based on discussion here:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/109631.html


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@293656 91177308-0d34-0410-b5e6-96231b3b80d8

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