auto merge of #16435 : vadimcn/rust/windows, r=pcwalton

Using "win32" to mean "Windows" is confusing, especially now, that Rust supports win64 builds.
Let's call spade a spade.

src/libstd/dynamic_lib.rs

@@ -278,7 +278,8 @@ pub mod dl {
     }
 }
 
-#[cfg(target_os = "win32")]
+#[cfg(target_os = "windows")]
+#[cfg(stage0, target_os = "win32")] // NOTE: Remove after snapshot
 pub mod dl {
     use c_str::ToCStr;
     use iter::Iterator;