Hello,

I am seeing a compilation error in alloc.c on line 3287 on Mac OS X due to
SPARE_MEMORY being undeclared.

Starting on line 193 of alloc.c is the following code block that attempts to
define SPARE_MEMORY.

#ifndef SYSTEM_MALLOC
/* Amount of spare memory to keep in large reserve block.  */

#define SPARE_MEMORY (1 << 14)
#endif

The problem is that SYSTEM_MALLOC is defined on Mac OS X but SPARE_MEMORY is
not defined in any of the system header files (at least running 'grep -RnH
SPARE_MEMORY *' in the /usr/include/ directory yields no results).  I
believe that the above code block should be changed to the following but I
am not certain how this change will affect other platforms.

#ifndef SPARE_MEMORY
/* Amount of spare memory to keep in large reserve block.  */

#define SPARE_MEMORY (1 << 14)
#endif

Note that SPARE_MEMORY does not appear to be defined on Windows either.  At
least I could not find it in any of the MinGW header files.

How is SPARE_MEMORY defined on systems that do define it?  Is the above
change the correct one?  It fixes the problem on Mac OS X but I do not want
to make a change that will cause problems for other operating systems.