/tt> and <TT>X86_64</tt>.
This is partially historical, and partially justified by the fact that there
are arguably more substantial architecture and ABI differences here than
for RISC variants.)
<P>
on GNU-based systems, <TT>cpp -dM empty_source_file.c</tt> seems to generate
a set of predefined macros.  On some other systems, the "verbose"
compiler option may do so, or the manual page may list them.
<LI>
A section that defines a small number of platform-specific macros, which are
then used directly by the 