Rollup of 11 pull requests

[tmandry]

Successful merges:

• Format libcore with rustfmt (including tests and benches) #66892 (Format libcore with rustfmt (including tests and benches))
• resolve: Resolve visibilities on fields with non-builtin attributes #67106 (resolve: Resolve visibilities on fields with non-builtin attributes)
• Print the visibility in print_variant. #67113 (Print the visibility in print_variant.)
• Simplify check_decl_no_pat. #67115 (Simplify check_decl_no_pat.)
• libstd miri tests: avoid warnings #67119 (libstd miri tests: avoid warnings)
• Added ExactSizeIterator bound to return types #67125 (Added ExactSizeIterator bound to return types)
• Simplify Layout::extend_packed #67138 (Simplify Layout::extend_packed)
• fix miri step debug printing #67145 (fix miri step debug printing)
• Do not ICE #67123 #67149 (Do not ICE ICE on rustc 1.41.0-nightly (ae1b871cc 2019-12-06) running on x86_64-pc-windows-msvc #67123)
• Move Layouts instead of binding by reference #67155 (Move Layouts instead of binding by reference)
• inline some common methods on OsStr #67169 (inline some common methods on OsStr)

Failed merges:

r? @ghost