Merge pull request #583 from RalfJung/c_unwind #777

Job	Run time
Clippy	14s
Rustfmt	14s
Test (aarch64-unknown-linux-gnu, ubuntu-latest, nightly)	2m 11s
Test (arm-unknown-linux-gnueabi, ubuntu-latest, nightly)	1m 52s
Test (arm-unknown-linux-gnueabihf, ubuntu-latest, nightly)	1m 56s
Test (i586-unknown-linux-gnu, ubuntu-latest, nightly)	1m 37s
Test (i686-unknown-linux-gnu, ubuntu-latest, nightly)	1m 34s
Test (powerpc-unknown-linux-gnu, ubuntu-latest, nightly)	2m 1s
Test (powerpc64-unknown-linux-gnu, ubuntu-latest, nightly)	2m 16s
Test (powerpc64le-unknown-linux-gnu, ubuntu-latest, nightly)	1m 55s
Test (thumbv6m-none-eabi, ubuntu-latest, nightly)	1m 29s
Test (thumbv7em-none-eabi, ubuntu-latest, nightly)	1m 25s
Test (thumbv7em-none-eabihf, ubuntu-latest, nightly)	1m 29s
Test (thumbv7m-none-eabi, ubuntu-latest, nightly)	1m 23s
Test (wasm32-unknown-unknown, ubuntu-latest, nightly)	1m 49s
Test (x86_64-unknown-linux-gnu, ubuntu-latest, nightly)	1m 36s
Test (x86_64-apple-darwin, macos-latest, nightly)	1m 45s
Test (i686-pc-windows-msvc, windows-latest, nightly)	2m 14s
Test (x86_64-pc-windows-msvc, windows-latest, nightly)	2m 17s
Test (i686-pc-windows-gnu, windows-latest, nightly-i686-gnu)	2m 42s
Test (x86_64-pc-windows-gnu, windows-latest, nightly-x86_64-gnu)	2m 59s
success	1s
	36m 59s

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