A small idea: reframe suggestions to be positive, future-looking, and pro-active, such as replacing:

did you forget to ‘#include <limits.h>’?

with:

  do you want to ‘#include <limits.h>’?

or, perhaps better:

  you may want to ‘#include <limits.h>’.

It may seem a small thing, but focusing on the solution rather than the problem may tend to sooth the mind of the coder, rather than to magnify their annoyance.

Consider it a path that is the opposite of Nedry's "You didn't say the magic word!"