Merge pull request #300 from ethereum/cpp-header-guards

cpp: Add missing '#pragma once' in evmc.hpp

include/evmc/evmc.hpp

@@ -2,6 +2,7 @@
  * Copyright 2018-2019 The EVMC Authors.
  * Licensed under the Apache License, Version 2.0.
  */
+#pragma once
 
 #include <evmc/evmc.h>
 #include <evmc/helpers.h>

test/integration/compilation/compilation_test.cxx

@@ -12,3 +12,12 @@
 #include <evmc/instructions.h>
 #include <evmc/loader.h>
 #include <evmc/utils.h>
+
+// Include again to check if headers have proper include guards.
+#include <evmc/evmc.h>
+#include <evmc/evmc.hpp>
+#include <evmc/helpers.h>
+#include <evmc/helpers.hpp>
+#include <evmc/instructions.h>
+#include <evmc/loader.h>
+#include <evmc/utils.h>