Building of blackbox fails, maybe related to libiconv

[ballapete (Peter "Pete" Dyballa)]

checking for sed... sed
checking for gencat... gencat
checking for iconv_open... no
checking for iconv_open in -liconv... no
checking for libiconv_open in -liconv... no
configure: error: Blackbox requires iconv(3) support.
Error: Target org.macports.configure returned: configure failure: shell command " cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_x11_blackbox/work/blackbox-0.70.1" && ./configure --prefix=/opt/local --disable-dependency-tracking --mandir=/opt/local/share/man --x-includes=/opt/local/include --x-libraries=/opt/local/lib " returned error 1
Command output: checking if /usr/bin/gcc-4.0 supports -fno-rtti -fno-exceptions... no

I've chosen the "universal" variant, which fails this incomprehensible way, but it is the same with the "darwin_7" variant (how can I retrieve details on the differences between the two variants?). Libiconv is installed:

 port list installed | egrep 'xorg-libXext|Xft2|expat|libiconv'
tclsh(63077,0xa0b1c820) malloc: Could not open , using stderr
expat                          @2.0.1          textproc/expat
libiconv                       @1.13           textproc/libiconv
Xft2                           @2.1.14         x11/Xft2
xorg-libXext                   @1.1.1          x11/xorg-libXext