First, install XCode Tools. Then install MacPorts, and use it to install: gcc and binutils.
sudo port -v selfupdateDownload and copy Q (download link on right), the OS X port of QEMU, into your Applications folder.
sudo port install i386-elf-gcc i386-elf-binutils
tar xfz gdb-6.8.tar.gz
cd gdb-6.8
./configure --target=i386-elf --disable-werror --program-prefix=i386-elf-
make
sudo make install
cd build
cp Makefile.mac Makefile