how the make "-I" option is passed to sub-makes

[Robert P. J. Day]

  i think i'm reading something incorrectly, but what is the proper
way to do a top-level invocation of

  $ make -Idir1 -Idir2 ...

and have those include options passed recursively to sub-makes?  i was
trying to do this with the MAKEFLAGS variable but i'm clearly doing
something wrong.

  i don't want to have to set that MAKEFLAGS variable explicitly in
the environment -- i want all include information to be supplied as
options to the make command itself.

rday