xcode-gcc

A plugin for XCode 6 that supports newer versions of GCC. Also works with XCode 7.3.

To install copy the plugin to

/Applications/Xcode.app/Contents/Plugins/Xcode3Core.ideplugin/Contents/SharedSupport/Developer/Library/Xcode/Plug-ins/

Full guide here:

http://hamelot.co.uk/programming/add-gcc-compiler-to-xcode-6/

Based off of https://code.google.com/p/xcode-gcc-plugin/ and modified for GCC 4.9

References: http://stackoverflow.com/questions/19061966/how-to-use-a-recent-gcc-with-xcode-5