Response from tech support: 

"GCC support within Thread will be included within our next stack release.  Keep an eye out for this in the next few weeks for its release.  We don't have an official date to give out."

When is Thread going to be supported in the GCC compiler? It sounds like this should be happening, but I am struggling to find a date when/if this will occur. Any help would be appreciated. 

Also, there is another forum post on this from a few months ago, but no one answered: http://community.silabs.com/t5/Proprietary/Zigbee-and-Thread-gcc-support/m-p/198440/highlight/true#M3124