document Makefile variables

GitOrigin-RevId: 5799b2d4f35a37f31897805d6312998be4177681
Change-Id: I752410de1b4c3b9ad80e34fb3e5b684d3fcbdf48
1 file changed
tree: e50e09fcd69fac2aadc5605321894716a8992ef8
  1. lib/