dmd build instructions from source don't work anymore

[Timothee Cour via Digitalmars-d]

git clone git://github.com/D-Programming-Language/dmd.git
cd dmd
make -f posix.mak MODEL=64

/Applications/Xcode.app/Contents/Developer/usr/bin/make -C src -f posix.mak
no cpu specified, assuming X86
dmd idgen.d
g++ -m64: No such file or directory
--- errorlevel 255
make[1]: *** [idgen] Error 255
make: *** [all] Error 2