I have been hunting down the last few pieces of code that made some
obsolete claims about not being able to use C99 yet or needing to be
compatible with pre-C99 or something like that. I found two obsolete
comments and two places where we could now actually use the C99
functionality that the comment was anticipating.
At least according to my grepping, all the remaining mentions of "C99"
are now up to date and relevant.