CodeGen: Remove implicit ilist iterator conversions, NFC

Finish removing implicit ilist iterator conversions from LLVMCodeGen.
I'm sure there are lots more of these in lib/CodeGen/*/.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249915 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed