attempt to fix error of
"cannot initialize variable of type 'char *'
with an rvalue type const char *

Index: tests/util/piglit-util.h
--- tests/util/piglit-util.h.orig
+++ tests/util/piglit-util.h
@@ -30,6 +30,7 @@ extern "C" {
 #endif
 
 #include "config.h"
+#include <string.h>
 
 #if defined(_WIN32)