Well, warnings are to show that something is wrong, and protecting includes with #error is right, at least in FreeBSD realm. Perhaps it's not a bad idea to use AC_INCLUDE_DEFAULTS or some other mechanism when checking a header with preprocessor (at least on FreeBSD).
I think that if the presence check makes no sense for this header, the four-argument version with AC_INCLUDES_DEFAULT should be used always.
OK, now to the patch: 1. It changes word "preprocessor" for "compiler" in AC_CHECK_HEADER comment.
Fine.
2. places AC_PREPROC_IFELSE before AC_COMPILE_IFELSE in _AC_CHECK_HEADER_MONGREL_BODY
I would like the maintainers of Autoconf to come back from holiday and comment on this one.
Paolo
