Rust

Add functions to allocate zeroed `Arc` and `Rc` (#283) #605

Job	Run time
Test with miri	1m 7s
Test on i686-unknown-linux-gnu with cross	1m 8s
Test Rust 1.34.0 on ubuntu-latest	1m 18s
Test with -Zsanitizer=address	40s
Test Rust stable on ubuntu-latest	8s
Test with -Zsanitizer=memory	40s
Test Rust beta on ubuntu-latest	14s
Test with -Zsanitizer=leak	40s
Test Rust nightly on ubuntu-latest	21s
Test Rust stable on macos-latest	11s
Test Rust stable on windows-latest	28s
Test Rust stable-x86_64-gnu on windows-latest	43s
Test Rust stable-i686-msvc on windows-latest	48s
Test Rust stable-i686-gnu on windows-latest	41s
	9m 7s

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