[PowerPC][NFC] Add a test case for extract and store patterns

An upcoming patch will change the codegen for these patterns. This test case is
added now so that the patch can show the differences in codegen.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344112 91177308-0d34-0410-b5e6-96231b3b80d8