glib/win32: Mark the function as windows only

Otherwise we fail to find std::os::windows when building docs

Author: bilelmoussaoui

glib-win32/src/functions.rs

@@ -4,6 +4,7 @@ use std::path::PathBuf;
 
 #[doc(alias = "g_win32_get_package_installation_directory_of_module")]
 #[doc(alias = "get_package_installation_directory_of_module")]
+#[cfg(all(docsrs, windows))]
 pub fn package_installation_directory_of_module(
     hmodule: std::os::windows::raw::HANDLE,
 ) -> Result<PathBuf, std::io::Error> {