Close-on-exec by default for received fds #53

Job	Run time
bare-cross-build (x86_64-unknown-openbsd)	27s
cross-ios-build (nightly, aarch64-apple-ios)	25s
native-test (nightly, ubuntu-latest, --all-features)	18s
cross-ios-build (nightly, x86_64-apple-ios)	19s
native-test (nightly, ubuntu-latest, --all-features --release)	15s
cross-ios-build (stable, aarch64-apple-ios)	11s
native-test (nightly, ubuntu-latest)	11s
cross-ios-build (stable, x86_64-apple-ios)	13s
native-test (nightly, macOS-latest, --all-features)	16s
native-test (nightly, macOS-latest, --all-features --release)	22s
native-test (nightly, macOS-latest)	16s
native-test (stable, ubuntu-latest, --all-features)	19s
native-test (stable, ubuntu-latest, --all-features --release)	6s
native-test (stable, ubuntu-latest)	8s
native-test (stable, macOS-latest, --all-features)	16s
native-test (stable, macOS-latest, --all-features --release)	12s
native-test (stable, macOS-latest)	10s
native-test (1.53.0, ubuntu-latest, --all-features)	1m 2s
native-test (1.53.0, ubuntu-latest, --all-features --release)	1m 0s
native-test (1.53.0, ubuntu-latest)	1m 0s
native-test (1.53.0, macOS-latest, --all-features)	1m 48s
native-test (1.53.0, macOS-latest, --all-features --release)	1m 7s
native-test (1.53.0, macOS-latest)	1m 20s
	11m 41s

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