windows: Add a common Windows header for platform specific wrappers

Include some more basic system headers in utils.h, so we can use that common
header on the different platforms.

src/libstrongswan/utils/chunk.h

@@ -30,6 +30,8 @@
 #include <alloca.h>
 #endif
 
+#include <utils/utils.h>
+
 typedef struct chunk_t chunk_t;
 
 /**