test/btstack_memory: fix test for newer gcc

src/btstack_memory.c

@@ -55,6 +55,11 @@
 
 #include <stdlib.h>
 
+#ifdef ENABLE_MALLOC_TEST
+extern "C" void * test_malloc(size_t size);
+#define malloc test_malloc
+#endif
+
 #ifdef HAVE_MALLOC
 typedef struct btstack_memory_buffer {
     struct btstack_memory_buffer * next;

test/btstack_memory/config_malloc/btstack_config.h

@@ -23,6 +23,6 @@
 #define HCI_INCOMING_PRE_BUFFER_SIZE 6
 
 // test hook to mock malloc
-#define malloc test_malloc
+#define ENABLE_MALLOC_TEST
 
 #endif