[make] add external/ to the module search list
[make] add external/ to the module search list

external/ will be where 3rd party code lives in the tree.

travisg/lk,minglun-tsai/lk,minglun-tsai/lk,ErikCorryGoogle/lk,sndnvaps/lk,sndnvaps/lk,hollanderic/lkstuff,travisg/lk,sndnvaps/lk,hollanderic/lkstuff,ErikCorryGoogle/lk,sndnvaps/lk,ErikCorryGoogle/lk,littlekernel/lk,minglun-tsai/lk,travisg/lk,hollanderic/lkstuff,sndnvaps/lk,littlekernel/lk,travisg/lk,minglun-tsai/lk,littlekernel/lk,littlekernel/lk,ErikCorryGoogle/lk,hollanderic/lkstuff