libraries a little by not passing all of ${CFLAGS} to lint. Pass
only options matching -[DIU]*. The important -nostdinc option can't
be passed like I first thought because lint misinterprets as
"-n -o stdinc". The unimportant -B* option can't be passed because
lint doesn't support it. Otherwise, we pass the same options as
to mkdep, exept for a bug in the latter: -U* is not passed. All
this depends on option args not being separated from option flags
by a space.