flo: Use GCC 4.7 for the kernel

Google is still using 4.6 for kernel building, but 4.7 worked fine for us with 4.4

Also clean up omni.dependencies and add GCC 4.7 to the dependencies

4.8, however, just crashes on boot once you get it to even compile

Change-Id: If9fd612dfc826655204292d93c28396c3b03c783