Add GNU/Hurd support #3267

Job	Run time
Check --no-default-features (nightly)	1m 15s
Check nightly-only targets (nightly)	36s
Check selected Tier 3 platforms (nightly)	5m 32s
Check (stable)	8m 23s
Rustfmt	16s
Check (nightly)	7m 43s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 30s
Check (1.63)	19m 52s
Test use-libc (ubuntu)	1m 7s
Test use-libc (i686-linux)	1m 27s
Test use-libc (aarch64-linux)	1m 37s
Test (ubuntu)	1m 12s
Test use-libc (powerpc64le-linux)	2m 13s
Test (ubuntu-20.04)	1m 13s
Test use-libc (riscv64-linux)	1m 45s
Test (i686-linux)	1m 44s
Test (aarch64-linux)	1m 33s
Test use-libc (arm-linux)	1m 36s
Test (powerpc64le-linux)	1m 50s
Test (riscv64-linux)	1m 46s
Test (s390x-linux)	1m 33s
Test (arm-linux)	2m 19s
Test (ubuntu-stable)	1m 17s
Test (i686-linux-stable)	1m 42s
Test (aarch64-linux-stable)	1m 40s
Test (riscv64-linux-stable)	1m 52s
Test (s390x-linux-stable)	1m 57s
Test (powerpc64le-linux-stable)	1m 41s
Test (arm-linux-stable)	1m 41s
Test (ubuntu-1.63)	4m 56s
Test (i686-linux-1.63)	4m 24s
Test (aarch64-linux-1.63)	4m 36s
Test (riscv64-linux-1.63)	4m 47s
Test (s390x-linux-1.63)	4m 31s
Test (powerpc64le-linux-1.63)	4m 37s
Test (arm-linux-1.63)	4m 26s
Test (macos-latest)	1m 40s
Test (macos-11)	1m 34s
Test (windows)	2m 44s
Test (windows-2019)	1m 14s
	1h 59m 21s

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