If you run bitbake -c menuconfig virtual/kernel in master (I tested with 19045bab71f45ec60a87aa6660be557de82072b2 to be exact, but I suspect latest master is still affected) it seems to be starting to build the entire kernel in the terminal session rather than just the few pieces it needs to build to start menuconfig.
Is this fixed by: [OE-core] [PATCH] cml1.bbclass: fix do_menuconfig ?
Yes, that patch fixes this.
Fixed in master by http://git.openembedded.org/openembedded-core/commit/?id=51c6ea30060eeddf93e4255cbd3847fc6aedaf9f
Verified with 23056103c949b498c23b47579e8dd57ce78e6ed9