py: Add #if guard around gc-specific code.
diff --git a/py/runtime.c b/py/runtime.c
index 71979c0..6efab04 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -1208,11 +1208,15 @@
 
 void *m_malloc_fail(size_t num_bytes) {
     DEBUG_printf("memory allocation failed, allocating " UINT_FMT " bytes\n", num_bytes);
-    if (gc_is_locked()) {
-        nlr_raise(mp_obj_new_exception_msg(& mp_type_MemoryError, 
+    if (0) {
+        // dummy
+    #if MICROPY_ENABLE_GC
+    } else if (gc_is_locked()) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_MemoryError,
                                            "memory allocation failed, heap is locked"));
+    #endif
     } else {
-        nlr_raise(mp_obj_new_exception_msg_varg(& mp_type_MemoryError, 
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_MemoryError,
                                                 "memory allocation failed, allocating " UINT_FMT " bytes", num_bytes));
     }
 }