CDRIVER-2719 add empty main for windows

Author: kevinAlbs

src/libmongoc/examples/example-resume.c

@@ -1,3 +1,5 @@
+#include <mongoc.h>
+
 #ifndef _WIN32
 /* An example implementation of custom resume logic in a change stream.
 * example-resume starts a client-wide change stream and persists the resume
@@ -9,8 +11,6 @@
 */
 #include <unistd.h>
 
-#include <mongoc.h>
-
 static const char *RESUME_TOKEN_PATH = "resume-token.json";
 
 static bool
@@ -160,4 +160,9 @@ main ()
    mongoc_cleanup ();
    return exit_code;
 }
+#else
+int main() {
+   printf("example-resume is not implemented on Windows.\n");
+   return 1;
+}
 #endif