fftw fails to build on Rosetta: Macports arch settings not respected

[barracuda156]

libtool: link: /usr/bin/gcc-4.2 -std=gnu99 -O3 -fomit-frame-pointer -fno-schedule-insns -fschedule-insns2 -fstrict-aliasing -Wl,-headerpad_max_install_names -Wl,-rpath -Wl,/opt/local/lib/libgcc -arch ppc -o .libs/fftw_test fftw_test.o test_main.o  -L/opt/local/lib ../fftw/.libs/libdfftw.dylib -lm
ld: warning: in fftw_test.o, file was built for unsupported file format which is not the architecture being linked (ppc)
ld: warning: in test_main.o, file was built for unsupported file format which is not the architecture being linked (ppc)
Undefined symbols:
  "_main", referenced from:
      start in crt1.10.5.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
make[1]: *** [fftw_test] Error 1