Add linting for `crate_type` attribute values.

This ensures that the `crate_type` attribute always contains a value,
and does not contain an invalid value.
libextra: Add benchmarks for ebml::reader::vuint_at()
libstd: Always inline all byteswap functions
fixup! libstd: Always inline all byteswap functions
auto merge of #11264 : am0d/rust/crate_type_lint, r=alexcrichton

This ensures that the `crate_type` attribute always contains a value,
and does not contain an invalid value.

Fixes #11256.
libsyntax: De-`@mut` `ParseSess::included_mod_stack`
librustc: De-`@mut` the parse session
libsyntax: De-`@mut` `StringReader::pos`
libsyntax: De-`@mut` `StringReader::last_pos`
libsyntax: De-`@mut` `StringReader::col`
libsyntax: De-`@mut` `StringReader::curr`
libsyntax: De-`@mut` `StringReader::peek_tok`
libsyntax: De-`@mut` `StringReader::peek_span`
libsyntax: De-`@mut` `TtReader::interpolations`
libsyntax: De-`@mut` `TtReader::repeat_idx`
libsyntax: De-`@mut` `TtReader::repeat_len`
libsyntax: De-`@mut` `TtReader::cur_tok`
libsyntax: De-`@mut` `TtReader::cur_span`
libsyntax: De-`@mut` `TtReader::stack`
libsyntax: De-`@mut` `StringReader`, `TtReader`, and `reader`