Disable the end guard for now.

The test for failing the end guard was always triggering (and was reported as
such in compiler warnings).  This is a temporary band-aid until I can work
out what's really going on.

Reviewed by:	obrien

lib/libstand/zalloc_defs.h

@@ -34,7 +34,9 @@
  */
 
 #define USEGUARD		/* use stard/end guard bytes */
+#if !defined(__powerpc__)
 #define USEENDGUARD
+#endif
 #define DMALLOCDEBUG		/* add debugging code to gather stats */
 #define ZALLOCDEBUG