[NFC][InstCombine] i65 tests for 'check for [no] signed truncation' pattern

Those initially broke chromium build:
https://bugs.llvm.org/show_bug.cgi?id=38204 and
https://crbug.com/864832

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337364 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed