Please search forum before posting something. This was discussed just a few weeks ago and is still on the opening page.
http://forums.amd.com/devforum/messageview.cfm?catid=390&threadid=157981&enterthread=y
I believe though if you do it properly, it can be more than two. I think you messed something up with paralellization. I have encountered similar issues with OpenMP, but not with building.