arch/sim: do not free memory of zero-length reallocation

Follow the change: apache#9151,
if MM_CUSTOMIZE_MANAGER is enabled, heap memory manager in host is used,
for example in sim:asan build.

malloc and related allocation APIs will fall back to host_realloc,
do not free memory of zero-length reallocation. So memory allocations
return valid pointer when request zero size in all sim build.

call stack:
    malloc()         (mm/umm_heap/umm_malloc.c)
    mm_malloc()      (arch/sim/src/sim/sim_heap.c)
    mm_realloc()     (arch/sim/src/sim/sim_heap.c)
    host_realloc()   (arch/sim/src/sim/posix/sim_hostmemory.c)
    host_memalign()  (arch/sim/src/sim/posix/sim_hostmemory.c)

Signed-off-by: fangxinyong <[email protected]>

Author: fxysunshine

arch/sim/src/sim/posix/sim_hostmemory.c

@@ -217,12 +217,7 @@ void *host_realloc(void *oldmem, size_t size)
   size_t oldsize;
   void *mem;
 
-  if (size == 0)
-    {
-      host_free(oldmem);
-      return NULL;
-    }
-  else if (oldmem == NULL)
+  if (oldmem == NULL)
     {
       return host_memalign(sizeof(void *), size);
     }