I just built Ikarus (revision 1747) on OS X 10.5.6 (x64) using GCC 4.2 from XCode 3.1.2, the only thing I had to do to make it build correctly was to provide CFLAGS="-arch x86_64" to ./configure:
Ikarus Scheme version 0.0.4-rc1+, 64-bit (revision 1747, build 2009-03-29) Copyright (c) 2006-2008 Abdulaziz Ghuloum /Patrik
