config.h as dependency

[Jason Sewall]

I have a project using autoconf + automake + autoheader, and clearly
the results of my builds depends on what is in config.h. Thus, I would
expect that when I run ./configure, everything in the build tree would
be marked as out-of-date and everything would be rebuilt - that is, I
would expect target to have @top_builddir@/config.h as an implicit
dependency.

I understand that running make clean && ./configure solves this
problem, but I was curious if there was a reasoning for this behavior.
Clearly, when not using AC_CONFIG_HEADERS, there is no such file to
place a dep. on and something else would have to note that things were
out-of-date.

Any thoughts? I've only been using autotools for a few months on just
a few projects and I don't have an expert command of how they work.

Jason