I'm preparing a tool-chain inside a fresh virtual machine and although the process pretty quickly informed me about the missing bison and flex binaries it was just when it was trying to patch the kernel sources (I believe) when it realized I didn't have a patch binary installed. I realize you might never early-check all dependencies for what-ever weird configuration options the user might have chosen, but as this is a pretty basic one I'm filing this as an enhancement.
Thanks, fixed in 7f7bf9637e2a9c3 (a few weeks ago)