Add missing includes.

Test: Builds.
Change-Id: Ia8b79154902503cdd774dc3b4523466123b4324c
diff --git a/libunwindstack/Global.cpp b/libunwindstack/Global.cpp
index 7a3de01..fdfd705 100644
--- a/libunwindstack/Global.cpp
+++ b/libunwindstack/Global.cpp
@@ -15,6 +15,7 @@
  */
 
 #include <stdint.h>
+#include <string.h>
 #include <sys/mman.h>
 
 #include <string>