[PatternMatch] Add matchers for vector operations

Summary:
There aren't any matchers for the three vector operations: insertelement, extractelement, and
shufflevector. This patch adds them as well as corresponding unit tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328709 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed