Revert "native,platform: use malloc/free for temporary memory"

This reverts commit 9249c3fb60.

* defining __NATIVE_USE_KLIB__ will link malloc() to the klib version,
  which may cause errors

am/src/native/platform.c

@@ -54,8 +54,8 @@ static void init_platform() {
       uintptr_t pad = (uintptr_t)vaddr & 0xfff;
       void *vaddr_align = vaddr - pad;
       uintptr_t size = phdr[i].p_memsz + pad;
-      void *temp_mem = malloc(size);
-      assert(temp_mem != NULL);
+      void *temp_mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+      assert(temp_mem != (void *)-1);
 
       // save data and bss sections
       memcpy(temp_mem, vaddr_align, size);
@@ -77,7 +77,9 @@ static void init_platform() {
       // restore the data in the sections
       memcpy_libc(vaddr_align, temp_mem, size);
 
-      free(temp_mem);
+      // unmap the temporary memory
+      ret2 = munmap(temp_mem, size);
+      assert(ret2 == 0);
     }
   }