rustc: feature gates errors should use the new attribute syntax
rustc: Improve errors on private static methods

This gives a better NOTE error message when a privacy error is encountered with
a static method. Previously no note was emitted (due to lack of support), but
now a note is emitted indicating that the struct/enum itself is private.

Closes #13641
rustdoc: Display tuple structs correctly

The fields of tuple structs recently gained the ability to have privacy
associated with them, but rustdoc was not updated accodingly. This moves the
struct field filtering to the rendering phase in order to preserve the ordering
of struct fields to allow tuple structs to have their private fields printed as
underscores.

Closes #13594
auto merge of #13639 : alexcrichton/rust/rustdoc-tuple-fields, r=sfackler

The fields of tuple structs recently gained the ability to have privacy
associated with them, but rustdoc was not updated accodingly. This moves the
struct field filtering to the rendering phase in order to preserve the ordering
of struct fields to allow tuple structs to have their private fields printed as
underscores.

Closes #13594
auto merge of #13647 : alexcrichton/rust/issue-13641, r=pcwalton

This gives a better NOTE error message when a privacy error is encountered with
a static method. Previously no note was emitted (due to lack of support), but
now a note is emitted indicating that the struct/enum itself is private.

Closes #13641
Fix call order to be the same as definition order
auto merge of #13650 : gmjosack/rust/master, r=alexcrichton

Feels strange to have the order be arbitrary here. Order them the same.
auto merge of #13652 : erickt/rust/master, r=alexcrichton