configure.in does:

>${SHELL} ./libtool --mode=compile ${CC} -shared \
>	-export-dynamic -o plugin.o plugin.c 2>&1 >/dev/null

and then uses plugin.o as part of a subsequent test. However, that libtool call is broken two ways, so the test section gives up well before actually doing $whatever with plugin.o. Building on OS X, I get:

checking for dlopen... yes
checking for dlsym... yes
/usr/libexec/gcc/powerpc-apple-darwin8/4.0.1/ld: unknown flag: -export-dynamic
collect2: ld returned 1 exit status

Yup, -export-dynamic is a flag for libtool --mode=link not --mode=compile. I have no idea what's really being tested next, but it looks like the AC_TRY_RUN program tries to dlopen the compiled object, which seems weird...shouldn't one be trying to dlopen a dynamic library of some sort rather than a simple .o?

But removing that flag doesn't help, because there's another mistake in the libtool syntax:

libtool: compile: unable to infer tagged configuration
libtool: compile: specify a tag with `--tag'

Need to pass a --tag=CC (I think that became a hard requirement as of libtool2?).