Don't depend on muslc for embedded artifacts.

These images are freestanding so should only use the standard headers
made available by the compiler in freestansing mode.

Change-Id: Id96db053d2c8571a95ece319578171c145894b50
diff --git a/src/mm.c b/src/mm.c
index 67a1332..813e1b9 100644
--- a/src/mm.c
+++ b/src/mm.c
@@ -16,10 +16,10 @@
 
 #include "hf/mm.h"
 
-#include <assert.h>
 #include <stdatomic.h>
 #include <stdint.h>
 
+#include "hf/assert.h"
 #include "hf/dlog.h"
 #include "hf/layout.h"