[GlobalISel][NFC] Regression test cases for aarch64 legalizer (s128 sext+icmp).

There were legalizer asserts in aarch64 globalisel (in debug mode) with s128
sext+icmp before r367060 and r366943 landed. These are just a couple reduced
mir and ir regression tests that came from a build where these were encountered.

llvm-svn: 370602