collector.  For simple ports, this is where most of
the effort is required.  We describe the macros below.
<P>
This section contains a subsection for each architecture (enclosed in a
suitable <TT>ifdef</tt>.  Each subsection usually contains some
architecture-dependent defines, followed by several sets of OS-dependent
defines, again enclosed in <TT>ifdef</tt>s.
<LI>
A section that fills in defaults for some macros left undefined in the preceding
section, and defines some other macros that rarely need adjust