[InstCombine] Add tests for fshl/fshr with masked operands; NFC

Baseline tests for D60660.

Patch by Shawn Landden.

Differential Revision: https://reviews.llvm.org/D60688

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358514 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed