refactor: I/O safety for unistd.rs (#2440) #76

Job	Run time
macos-aarch64	1m 48s
minver	15s
linux_native_builds (x86_64-unknown-linux-gnu)	3m 4s
rust_stable	1m 21s
macos	3m 41s
linux_native_builds (x86_64-unknown-linux-musl)	2m 29s
rustfmt	18s
tier3 (x86_64-unknown-dragonfly)	1m 3s
tier3 (x86_64-unknown-openbsd)	57s
redox	33s
cross (arm-unknown-linux-gnueabi)	1m 36s
cross_compiling (aarch64-linux-android)	33s
cross (armv7-unknown-linux-gnueabihf)	2m 13s
cross_compiling (arm-linux-androideabi)	34s
cross (i686-unknown-linux-gnu)	1m 41s
cross_compiling (armv7-linux-androideabi)	32s
cross (i686-unknown-linux-musl)	1m 46s
cross_compiling (i686-linux-android)	33s
cross (mips-unknown-linux-gnu)	1m 41s
cross_compiling (x86_64-linux-android)	39s
cross (mips64-unknown-linux-gnuabi64)	2m 7s
cross_compiling (arm-unknown-linux-musleabi)	42s
cross (mips64el-unknown-linux-gnuabi64)	1m 37s
cross_compiling (x86_64-unknown-fuchsia)	26s
cross_compiling (x86_64-unknown-illumos)	33s
cross (mipsel-unknown-linux-gnu)	1m 42s
cross_compiling (aarch64-apple-ios, true)	29s
cross (powerpc64le-unknown-linux-gnu)	1m 58s
cross_compiling (powerpc64-unknown-linux-gnu)	34s
cross_compiling (s390x-unknown-linux-gnu)	33s
cross_compiling (x86_64-unknown-linux-gnux32)	35s
cross_compiling (x86_64-unknown-netbsd)	27s
	39m 0s

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