m4conf obviously has messy configure scripts; they are just written in m4. For instance, it somes with a 120 kilobyte file m4sugar which is fully of m4 cruft.
Oh look, m4sugar.m4 is taken from GNU Autoconf and is GPLv3. The. m4conf project's master license doesn't mention this; it's a "BSD1" type license (like BSD2, but with no requirement for the copyright notice to appear in documentation or accompanying materials). Oops!
m4sugar says that it requires GNU m4, not just any POSIX m4.
I wrote the configure script in shell because that's what I decided I can depend on being present in the target systems. I deliberately rejected any approach involving m4 to show that a GNU style configure script can be obtained in as straightforward way, without convoluted metaprogramming.
There is a lot of copy-paste programming in my configure script, but it doesn't have to be that way; a script of this type can be better organized than my example. Anyway, you're not significantly disadvantaged writing in shell compared to m4, especially if you're mostly interested in probing the environment, not complex text generation.
I don't think that it's enough to test for header files being present. Almost all my tests target library features: including a header, calling some functions and actually linking a program. The contents of headers vary from system to system and with compiler options.
