gprolog can't compile on Snow Leopard

[mellon85@…]

gprolog can't compile on Snow Leopard due to some compiler options

--->  Computing dependencies for gprolog
--->  Fetching gprolog
--->  Attempting to fetch gprolog-1.3.1.tar.gz from http://www.gprolog.org/
--->  Verifying checksum(s) for gprolog
--->  Extracting gprolog
--->  Configuring gprolog
--->  Building gprolog
Error: Target org.macports.build returned: shell command " cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_lang_gprolog/work/gprolog-1.3.1/src" && /usr/bin/make -j2 all " returned error 2
Command output: (cd EnginePl; /usr/bin/make config)
/usr/bin/gcc-4.2 -march=i486 -O3 -fomit-frame-pointer  -o pl_config pl_config.c
pl_config.c:1: error: CPU you selected does not support x86-64 instruction set
pl_config.c:1: error: CPU you selected does not support x86-64 instruction set
make[1]: *** [pl_config] Error 1
make: *** [all] Error 2