In Thumb1 mode, the custom lowering for ARMISD::CMPZ could never emit tADDi3

Reviewers: jmolloy, t.p.northover

Reviewed By: t.p.northover

Subscribers: t.p.northover, aemerson, rengolin, llvm-commits

Differential Revision: https://reviews.llvm.org/D30097

llvm-svn: 295478