more compatibility with other platforms (#1110)
more compatibility with other platforms (#1110)

Motivation:

Everything should compile on as many platforms as possible.

Modifications:

Guard FileManager.temporaryDirectory behind
`#available(macOS 10.12, iOS 10, tvOS 10, watchOS 3, macCatalyst 13, *)`
instead of just macOS 10.12.

Result:

Tests should build on iOS and friends too.
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio