Add missing includes.

Change-Id: Ibf549266a19a67eb9158d341a69dddfb654be669
diff --git a/linker/linker_phdr.cpp b/linker/linker_phdr.cpp
index af4dc25..91a2fb8 100644
--- a/linker/linker_phdr.cpp
+++ b/linker/linker_phdr.cpp
@@ -29,6 +29,7 @@
 #include "linker_phdr.h"
 
 #include <errno.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <sys/stat.h>