SystemZInstrInfo.cpp: Tweak an assertion. [-Wunused-variable]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185499 91177308-0d34-0410-b5e6-96231b3b80d8
Avoid doing a lot of computation when we have multiple ranges and
avoid adding information for the debug_inlined section when it isn't
going to be emitted anyhow.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185500 91177308-0d34-0410-b5e6-96231b3b80d8