fix lib.rs so that it builds on all three targeted platforms

src/lib.rs

@@ -1,12 +1,14 @@
-mod win;
-
-pub use win::*;
-
 use std::ffi::c_void;
 
+#[cfg(target_os = "windows")]
+mod win;
+#[cfg(target_os = "windows")]
+pub use win::*;
+#[cfg(target_os = "linux")]
 mod x11;
-
+#[cfg(target_os = "macos")]
 mod macos;
+#[cfg(target_os = "macos")]
 pub use macos::Window;
 
 pub enum Parent {
@@ -24,6 +26,7 @@ pub struct WindowOpenOptions<'a> {
     pub parent: Parent,
 }
 
+#[cfg(target_os = "linux")]
 pub fn run(options: WindowOpenOptions) {
     x11::run(options);
 }