[AMDGPU] Add test case on crashing of `si-lower-sgpr-spills` pass

Reviewers: arsenm

Subscribers: qcolombet, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64273

llvm-svn: 366602