Both "product" and "build" ordering are rampant in /usr/src. This document
is not indented to be as strict as style(9) as historically BSD hasn't been
as consistent about Makefile as C code. Also there are too many variations,
exceptions and allowances in out existing Makefile style to be strict.
However there is a general level of consensus on what the general BSD style
of our Makefiles is. This manpage documents that "smell".
o Give the proper spelling for WARNS.
o Clarify using NO_WERROR.
o Embelish -D after -I verbage.
o Document preference of ${.ALLSRC} & ${.TARGET} vs. $< & $@.
Based on: brucification
