> Note that cmathmodule.c compiles fine and that does reference
> log1p() too.

Now that's *really* peculiar.  I can't imagine why one would work and
the other not.  Some ideas about how to proceed from here:

- try doing a debug build (./configure --with-pydebug) to see if
  the errors still occur.  (They probably will, but you never know...)

- What happens if you add an

#include <float.h>

after the line

#include "Python.h"

in mathmodule.c?  I'm clutching at straws here, but that's the only
difference I can see between cmathmodule.c and mathmodule.c that might
be affecting this.  Your error output from gcc looks as though either:

- math.h isn't being included, or
- you've got more than one version of math.h, and the wrong one's
  being included, or
- math.h doesn't declare log1p (but you've already said that it does).

What *should* be happening is that the line

#include "Python.h"

includes Python.h, which in turn includes pyport.h, which in turn
includes math.h.

It's also odd that this is the first function that fails.  If math.h
isn't being included somehow, then I'd also expect acosh, etc. to be
failing to build.

Do people really still use m68k. :-)