Rollup merge of #40457 - frewsxcv:frewsxcv-macos, r=steveklabnik

Update usages of 'OSX' (and other old names) to 'macOS'.

As of last year with version 'Sierra', the Mac operating system is now
called 'macOS'.

diff --cc src/bootstrap/lib.rs
Simple merge

diff --cc src/libstd/sys/unix/ext/net.rs
Simple merge