Use more constants and functions from libc #192

Job	Run time
aarch64-apple-darwin	48s
aarch64-apple-darwin force-inprocess	58s
aarch64-apple-darwin async	54s
x86_64-apple-darwin	1m 31s
x86_64-apple-darwin force-inprocess	1m 24s
x86_64-apple-darwin async	1m 22s
x86_64-unknown-linux-gnu	53s
x86_64-unknown-linux-gnu force-inprocess	54s
x86_64-unknown-linux-gnu async	1m 4s
x86_64-pc-windows-msvc	1m 44s
x86_64-pc-windows-msvc force-inprocess	1m 45s
x86_64-pc-windows-msvc async	2m 19s
i686-pc-windows-msvc	2m 16s
i686-pc-windows-msvc force-inprocess	2m 32s
i686-pc-windows-msvc async	2m 20s
x86_64-unknown-linux-gnu memfd	54s
Result	1s
	23m 39s

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