[ Not intended for commit. I'm just posting it to back up an
RFC on cfe-dev. ]
This patch follows on from the main sizeless type patch and adds
comments explaining why some code didn't change. It avoids adding
comments for Objective C/C++ and OpenMP since the sizeless type feature
is at the moment restricted to core C and C++. It also avoids adding
comments for code specific to the Microsoft ABI, which at present
doesn't support sizeless types.