windows: Use WINAPI call convention for Windows API callbacks

For x86_64 it does not actually matter, but for i686 builds the call convention
is different with WINAPI.

src/libstrongswan/utils/utils.c

@@ -247,7 +247,7 @@ static mutex_t *sigint_mutex;
 /**
  * Control handler to catch ^C
  */
-static BOOL handler(DWORD dwCtrlType)
+static BOOL WINAPI handler(DWORD dwCtrlType)
 {
 	switch (dwCtrlType)
 	{

src/libstrongswan/utils/windows.h

@@ -116,14 +116,14 @@ char* strndup(const char *s, size_t n);
  * Provided via ws2_32
  */
 #ifndef InetNtop
-const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);
+const char WINAPI *inet_ntop(int af, const void *src, char *dst, socklen_t size);
 #endif
 
 /**
  * Provided via ws2_32
  */
 #ifndef InetPton
-int inet_pton(int af, const char *src, void *dst);
+int WINAPI inet_pton(int af, const char *src, void *dst);
 #endif
 
 /**