Fix Windows Ctrl Handler declaration

The handler function signature must include the calling convention
declaration.

Ref: <https://stackoverflow.com/questions/61717439/why-calling-setconsolectrlhandler-triggers-a-warning>

app/src/scrcpy.c

@@ -50,7 +50,7 @@ static struct input_manager input_manager = {
 };
 
 #ifdef _WIN32
-BOOL windows_ctrl_handler(DWORD ctrl_type) {
+BOOL WINAPI windows_ctrl_handler(DWORD ctrl_type) {
     if (ctrl_type == CTRL_C_EVENT) {
         SDL_Event event;
         event.type = SDL_QUIT;