Build qt application with g++ 4.5 on mac

[manifest]

I try to compile application:

#include <QtCore>
#include <QCoreApplication>

int main(int argc, char **argv)
{
QCoreApplication app(argc, argv);
app.exec();
}

and receive this error:
cc1plus: error: unrecognized command line option "-arch"

How i can solve it?

---
macosx 10.6
gcc version 4.5.0 20100211 (experimental) (GCC) from macports
qt 4.6.2, compile with gcc version 4.2.1 (Apple Inc. build 5646)