Replace traditional header guards with pragma once.

src/_strops.hpp

@@ -5,8 +5,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
-#ifndef WOMBAT_FS_STROPS_HPP
-#define WOMBAT_FS_STROPS_HPP
+#pragma once
 
 namespace wombat {
 namespace fs {
@@ -15,5 +14,3 @@ int strcmp(const char *str1, const char *str2);
 
 }
 }
-
-#endif