o Provide $(obj),$(objtree) and friends in the top-level Makefile as well
  for consistency (Sam Ravnborg)
o Make $(call cmd,whatever) consistent with $(call if_changed,whatever),
  i.e. both will execute $(cmd_whatever)
o Add $(echo_target), which will print the current target in a suitable
  way for the quiet output format (i.e. target name relative to the
  top-level directory)
o Fix the dependencies for host compiled programs to work for files in
  subdirectories (missed converting them when introducing $(depfile))
o Add commands which will be useful when generating boot images.