In ext/gd/gdcache.h, line 43-47, the code says

#ifndef _OSD_POSIX
#include <malloc.h>
#else
#include <stdlib.h> /* BS2000/OSD defines malloc() & 
friends in stdlib.h */
#endif

However, under MacOS X Public Beta, [1] _OSD_POSIX 
is not defined by the compiler (at least not to my 
knowledge), and [2] there is no /usr/include/malloc.h.  
These two conditions lead to a compile failure.

Now, by looking at the configure process, I noticed that 
there is a check for the existence of malloc.h  Perhaps 
this file can be modified to use this check or some 
other instead?