Add missing includes.

Test: Builds.
Change-Id: Ia8b79154902503cdd774dc3b4523466123b4324c
diff --git a/libunwindstack/Memory.cpp b/libunwindstack/Memory.cpp
index a30d65e..9904fef 100644
--- a/libunwindstack/Memory.cpp
+++ b/libunwindstack/Memory.cpp
@@ -16,6 +16,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/ptrace.h>
 #include <sys/stat.h>