e end of the main data segment.  Defaults to <TT>end</tt>,
where that is declared as an array.  This works in some cases, since
the linker introduces a suitable symbol.
<DT><TT>DATASTART2, DATAEND2</tt>
<DD>
Some platforms have two discontiguous main data segments, e.g.
for initialized and uninitialized data.  If so, these two macros
should be defined to the limits of the second main data segment.
<DT><TT>STACK_GROWS_UP</tt>
<DD>
Should be defined if the stack (or thread stacks) grow towards higher
addresse