refactor divrem8 lowering; NFCI

The code duplication contributed to PR25754:
https://llvm.org/bugs/show_bug.cgi?id=25754


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256957 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed