malloc.h: use sysconf(_SC_PAGESIZE) instead of __pagesize

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/stdlib/malloc/malloc.h

@@ -20,8 +20,7 @@
   (__alignof__ (double) > sizeof (size_t) ? __alignof__ (double) : sizeof (size_t))
 
 /* The system pagesize... */
-extern size_t __pagesize;
-#define MALLOC_PAGE_SIZE	__pagesize
+#define MALLOC_PAGE_SIZE	sysconf(_SC_PAGESIZE)
 
 /* The minimum size of block we request from the the system to extend the
    heap for small allocations (we may request a bigger block if necessary to