This problem occurs when compiling --with-DOM to build in the libxml support.

using
libxml 2.2.1 compiled with
zlib 1.1.3 and
libiconv 1.3

libxml can be compiled in a number of ways, and looking at the config.m4 file in ext/domxml I think it is assumed that only the libz library has been used.  If I specifically compile libxml without iconv support, then PHP compiles fine.  With libxml compiled with iconv support, configure fails because of the unresolved references in libxml to functions in libiconv.

I don't really understand the contents of the config.m4 file in ext/domxml, but I managed to fix this to get PHP to complile with libxml and iconv support by adding -liconv to the LIBS= in line 16, and adding a new line AC_ADD_LIBRARY(iconv) after line 20.  I know this isn't the right way to do it because the checks should be made for libiconv in the same way as they are for zlib.  However, after doing a buildconf this was enought to get PHP to compile and build as an Apache module, so I guess someone who knows what they're doing could sort it with this information :-)

Regards  -  Nick