Handle *_EXTEND_VECTOR_INREG during Integer Legalization

Summary:
These nodes need legalization for 3-element vectors.  This commit
handles the legalization and adds tests for zext and sext.

This fixes PR30614.

Reviewers: RKSimon, srhines

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D25268

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@283496 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed