Add missing includes.

Change-Id: Ibf549266a19a67eb9158d341a69dddfb654be669
diff --git a/libc/bionic/malloc_debug_common.cpp b/libc/bionic/malloc_debug_common.cpp
index 38c6583..1a2765a 100644
--- a/libc/bionic/malloc_debug_common.cpp
+++ b/libc/bionic/malloc_debug_common.cpp
@@ -41,6 +41,7 @@
 
 #include <pthread.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 
 #include "private/ScopedPthreadMutexLocker.h"