kernel-wfp: Fix/Complete some fwpuclnt functionality in MinGW

While MinGW declares all the required symbols, some of them are missing in the
library files. We provide missing variables locally, functions get a stub
that call the GetProcAddress()ed function from the DLL.

Also some MinGW headers define some enum values incorrectly, we overload these
using defines.

src/libcharon/plugins/kernel_wfp/kernel_wfp_ipsec.c

@@ -16,6 +16,7 @@
 /* Windows 7, for some fwpmu.h functionality */
 #define _WIN32_WINNT 0x0601
 
+#include "kernel_wfp_compat.h"
 #include "kernel_wfp_ipsec.h"
 
 #include <daemon.h>
@@ -23,9 +24,6 @@
 #include <collections/array.h>
 #include <collections/hashtable.h>
 
-#include <fwpmtypes.h>
-#include <fwpmu.h>
-#undef interface
 
 typedef struct private_kernel_wfp_ipsec_t private_kernel_wfp_ipsec_t;