Add GNU/Hurd support #221

Job	Run time
cross-ios-build (nightly, aarch64-apple-ios)	22s
native-test (nightly, ubuntu-latest)	22s
windows-test (nightly, x86_64-pc-windows-gnu)	3m 44s
native-test (nightly, windows-latest)	3m 23s
bare-cross-build (nightly, x86_64-unknown-haiku)	34s
windows-test (nightly, i686-pc-windows-gnu)	5m 7s
native-test (nightly, macOS-latest)	56s
native-test (stable, ubuntu-latest)	25s
windows-test (stable, x86_64-pc-windows-gnu)	5m 53s
bare-cross-build (nightly, x86_64-unknown-openbsd)	36s
native-test (stable, windows-latest)	4m 24s
windows-test (stable, i686-pc-windows-gnu)	3m 43s
bare-cross-build (nightly, x86_64-unknown-redox)	32s
native-test (stable, macOS-latest)	1m 23s
bare-cross-build (nightly, x86_64-fuchsia)	46s
native-test (1.48.0, ubuntu-latest)	3m 11s
cross-ios-build (nightly, x86_64-apple-ios)	31s
bare-cross-build (nightly, wasm32-unknown-unknown)	31s
native-test (1.48.0, windows-latest)	8m 20s
cross-ios-build (stable, aarch64-apple-ios)	23s
native-test (1.48.0, macOS-latest)	3m 39s
cross-ios-build (stable, x86_64-apple-ios)	30s
	49m 15s

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