Two changes. One from Shaun Jackman makes libbb/interface.c compile only if

Two changes.  One from Shaun Jackman makes libbb/interface.c compile only if
it's going to be used.  (I'm guessing it doesn't work with newlib.)

The other one is from me: allyesconfig shouldn't enable devfs because that
changes all sorts of unrelated stuff (like /dev/loop0->dev/loop/0), which
can come as a bit of a surprise.  (It's still there, but you have to go into
menuconfig and select it manually.)