Use cfg(target_has_atomic) on no-std targets #2414

Job	Run time
cargo clippy	26s
cargo bench	53s
cargo +1.36 build (futures-{core, io, sink})	31s
cargo +stable build	43s
cargo hack check --feature-powerset	2m 26s
cargo +beta build	43s
cargo fmt	11s
cargo minimal-versions build	25s
cargo +nightly build	44s
cargo miri test	8m 27s
cargo build --target thumbv7m-none-eabi	29s
cargo test -Z sanitizer=address	5m 39s
cargo build --target thumbv6m-none-eabi	26s
cargo test (ubuntu-latest)	3m 8s
cargo test -Z sanitizer=memory	4m 1s
cargo +1.56 build	1m 23s
cargo test (macos-latest)	4m 57s
cargo test -Z sanitizer=thread	2m 47s
cargo test (windows-latest)	4m 55s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	3m 27s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	6m 29s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	7m 4s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	3m 37s
	1h 3m 51s

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