Add missing includes.

Test: Builds.
Change-Id: Ia8b79154902503cdd774dc3b4523466123b4324c
diff --git a/libunwindstack/Maps.cpp b/libunwindstack/Maps.cpp
index 8729871..a9fb859 100644
--- a/libunwindstack/Maps.cpp
+++ b/libunwindstack/Maps.cpp
@@ -19,6 +19,7 @@
 #include <inttypes.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <unistd.h>