Rolling up PRs in the queue

Closes #14797 (librustc: Fix the issue with labels shadowing variable names by making)
Closes #14823 (Improve error messages for io::fs)
Closes #14827 (libsyntax: Allow `+` to separate trait bounds from objects.)
Closes #14834 (configure: Don't sync unused submodules)
Closes #14838 (Remove typo on collections::treemap::UnionItems)
Closes #14839 (Fix the unused struct field lint for struct variants)
Closes #14840 (Clarify `Any` docs)
Closes #14846 (rustc: [T, ..N] and [T, ..N+1] are not the same)
Closes #14847 (Audit usage of NativeMutex)
Closes #14850 (remove unnecessary PaX detection)
Closes #14856 (librustc: Take in account mutability when casting array to raw ptr.)
Closes #14859 (librustc: Forbid `transmute` from being called on types whose size is)
Closes #14860 (Fix `quote_pat!` & parse outer attributes in `quote_item!`)