Refactor creation of overflow result tuples in InstCombineCalls.

Extract the creation of overflow result tuples in a separate function. NFC.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224006 91177308-0d34-0410-b5e6-96231b3b80d8
test commit (spelling correction)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224007 91177308-0d34-0410-b5e6-96231b3b80d8