Hi Bart!
Surfing around the web gave me the solution :
http://apple.stackexchange.com/questions/58186/how-to-compile-mod-wsgi-mod-fastcgi-etc-on-mountain-lion-by-fixing-apxserror
i.e. sudo ln -s /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/ /Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.8.xctoolchain

It works...
Thanks you all!