Let dlfcn.h return a function pointer on Windows

lib/roken/dlfcn.h

@@ -42,7 +42,11 @@
 #endif
 #endif
 
+#ifdef _WIN32
+typedef int (__stdcall *DLSYM_RET_TYPE)();
+#else
 #define DLSYM_RET_TYPE void *
+#endif
 
 #ifdef __cplusplus
 extern "C" 

lib/roken/dlfcn_w32.c

@@ -91,6 +91,6 @@ dlsym(void * vhm, const char * func_name)
 {
     HMODULE hm = (HMODULE) vhm;
 
-    return GetProcAddress(hm, func_name);
+    return (DLSYM_RET_TYPE)(ULONG_PTR)GetProcAddress(hm, func_name);
 }