Add GNU/Hurd support #991

Job	Run time
Clippy	19s
Check (armv7-sony-vita-newlibeabihf)	31s
Check (aarch64-apple-ios)	9s
Check (i686-unknown-hurd-gnu)	28s
Docs (aarch64-apple-ios)	15s
Check (aarch64-linux-android)	11s
Docs (armv7-sony-vita-newlibeabihf)	27s
Docs (aarch64-linux-android)	20s
Check (x86_64-apple-darwin)	8s
Docs (i686-unknown-hurd-gnu)	26s
Rustfmt	9s
Docs (x86_64-apple-darwin)	15s
Check (x86_64-unknown-fuchsia)	9s
Docs (x86_64-unknown-fuchsia)	20s
Check (x86_64-pc-windows-msvc)	9s
Docs (x86_64-pc-windows-msvc)	13s
Check (x86_64-pc-solaris)	21s
Test (stable)	21s
Docs (x86_64-pc-solaris)	22s
Check (x86_64-unknown-freebsd)	15s
Test (1.63.0)	6m 21s
Docs (x86_64-unknown-freebsd)	19s
Check (x86_64-unknown-illumos)	23s
Test (beta)	20s
Docs (x86_64-unknown-illumos)	14s
Check (x86_64-unknown-linux-gnu)	20s
Test (nightly)	39s
Docs (x86_64-unknown-linux-gnu)	17s
Check (x86_64-unknown-linux-musl)	12s
Test (macos)	47s
Docs (x86_64-unknown-linux-musl)	22s
Check (x86_64-unknown-netbsd)	18s
Test (windows)	2m 1s
Docs (x86_64-unknown-netbsd)	18s
Check (x86_64-unknown-redox)	20s
Docs (x86_64-unknown-redox)	19s
Check (armv7-linux-androideabi)	8s
Docs (armv7-linux-androideabi)	16s
Check (i686-linux-android)	29s
Docs (i686-linux-android)	18s
	20m 29s

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