CodeGen: Remove implicit iterator conversions from SlotIndexes.h, NFC
CodeGen: Remove implicit iterator conversions from SlotIndexes.h, NFC

Be explicit about changes between pointers and iterators, as with other
recent commits.  This transitively removes implicit ilist iterator
conversions from about 20 source files in CodeGen.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@249869 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm