Introduce set_errno #634

Job	Run time
rust_stable	1m 2s
macos	1m 40s
linux_native_builds (x86_64-unknown-linux-gnu)	1m 24s
minver	16s
linux_native_builds (x86_64-unknown-linux-musl)	1m 20s
rustfmt	13s
tier3 (x86_64-unknown-dragonfly)	1m 0s
tier3 (x86_64-unknown-openbsd)	58s
tier3 (x86_64-unknown-haiku)	53s
tier3 (i686-unknown-hurd-gnu)	59s
redox	34s
cross (arm-unknown-linux-gnueabi)	1m 41s
cross_compiling (aarch64-linux-android)	33s
cross_compiling (arm-linux-androideabi)	35s
cross (armv7-unknown-linux-gnueabihf)	1m 47s
cross (i686-unknown-linux-gnu)	1m 35s
cross_compiling (armv7-linux-androideabi)	36s
cross (i686-unknown-linux-musl)	1m 45s
cross_compiling (i686-linux-android)	33s
cross (mips-unknown-linux-gnu)	1m 53s
cross_compiling (x86_64-linux-android)	33s
cross_compiling (arm-unknown-linux-musleabi)	33s
cross_compiling (x86_64-unknown-fuchsia)	29s
cross (mips64-unknown-linux-gnuabi64)	1m 45s
cross_compiling (x86_64-unknown-illumos)	29s
cross (mips64el-unknown-linux-gnuabi64)	1m 40s
cross_compiling (aarch64-apple-ios, true)	33s
cross (mipsel-unknown-linux-gnu)	1m 41s
cross_compiling (powerpc64-unknown-linux-gnu)	40s
cross (powerpc64le-unknown-linux-gnu)	1m 49s
cross_compiling (s390x-unknown-linux-gnu)	35s
cross_compiling (x86_64-unknown-linux-gnux32)	39s
cross_compiling (x86_64-unknown-netbsd)	28s
	33m 11s

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