Added some missing cstring includes

projects/SelfTest/String.tests.cpp

@@ -2,6 +2,8 @@
 
 #include "catch.hpp"
 
+#include <cstring>
+
 TEST_CASE( "String", "[Strings]" ) {
     using Catch::String;
     

projects/SelfTest/StringRef.tests.cpp

@@ -3,6 +3,8 @@
 
 #include "catch.hpp"
 
+#include <cstring>
+
 namespace Catch {
 
     // Implementation of test accessors