Add missing includes.

Change-Id: Ibf549266a19a67eb9158d341a69dddfb654be669
diff --git a/libc/bionic/malloc_debug_qemu.cpp b/libc/bionic/malloc_debug_qemu.cpp
index 2f4949b..fa40b35 100644
--- a/libc/bionic/malloc_debug_qemu.cpp
+++ b/libc/bionic/malloc_debug_qemu.cpp
@@ -45,6 +45,7 @@
 #include <stdlib.h>
 #include <stddef.h>
 #include <stdio.h>
+#include <string.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/param.h>