zmalloc: switch back to slower fit first alloc at the beginning of block

because it has less memory fragmentation and is able to load ls.asm with
pound. faster alloc gave out-of-memory, with 30kB free - 10kB
application, should be able to fit 10kB source code(!).

lib/zmalloc.c

@@ -60,7 +60,7 @@ void *zmalloc(size_t size) {
     if (!p) return NULL;
 
     if (p->size - size > block_info_size) {
-#if 0
+#if 1
         // split, alloc at begin
         struct block_info *q = (void *) p + block_info_size + size;
         q->next = p->next;
@@ -71,7 +71,7 @@ void *zmalloc(size_t size) {
         p->size = size;
         q->free = 1;
 #endif
-#if 1
+#if 0
         // split, alloc at end
         struct block_info *q = (void *) p + p->size - size;
         p->size -= size + block_info_size;