Forgot "#pragma once" macro in some mingw compat header files

Signed-off-by: falkTX <falktx@falktx.com>

include/mingw-compat/Shlobj.h

@@ -1,6 +1,6 @@
 /*
  * DISTRHO Cardinal Plugin
- * Copyright (C) 2021 Filipe Coelho <falktx@falktx.com>
+ * Copyright (C) 2021-2022 Filipe Coelho <falktx@falktx.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -15,4 +15,6 @@
  * For a full copy of the GNU General Public License see the LICENSE file.
  */
 
+#pragma once
+
 #include <shlobj.h>

include/mingw-compat/Shlwapi.h

@@ -1,6 +1,6 @@
 /*
  * DISTRHO Cardinal Plugin
- * Copyright (C) 2021 Filipe Coelho <falktx@falktx.com>
+ * Copyright (C) 2021-2022 Filipe Coelho <falktx@falktx.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -15,4 +15,6 @@
  * For a full copy of the GNU General Public License see the LICENSE file.
  */
 
+#pragma once
+
 #include <shlwapi.h>