Don't test the rustdoc rendering context size on Windows.

This assert is just making sure the size of `Context` doens't grow
unexpectedly, and it's already not being checked on every platform.

`PathBuf` now has a different size on Windows, so adjust this to
avoid checking the size on Windows.

Author: sunfishcode

src/librustdoc/html/render/context.rs

@@ -71,7 +71,7 @@ pub(crate) struct Context<'tcx> {
 }
 
 // `Context` is cloned a lot, so we don't want the size to grow unexpectedly.
-#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+#[cfg(all(not(windows), target_arch = "x86_64", target_pointer_width = "64"))]
 rustc_data_structures::static_assert_size!(Context<'_>, 128);
 
 /// Shared mutable state used in [`Context`] and elsewhere.