Fix unexpected_cfgs warnings. #1669

Job	Run time
Rustfmt	7s
Check Cross-Compilation (stable)	1m 15s
Check Cross-Compilation (beta)	1m 24s
Check Cross-Compilation on Rust nightly on Windows (nightly)	1m 25s
Check Cross-Compilation on Rust nightly (nightly)	1m 53s
Check Cross-Compilation on Windows (stable)	2m 37s
Check Cross-Compilation on Windows (beta)	1m 12s
Fuzz Targets	46s
Test (stable)	25s
Test (windows-latest)	2m 6s
Test linux-raw support (ubuntu)	29s
Test (msrv)	1m 57s
Test (windows-2019)	1m 57s
Test linux-raw support (ubuntu-20.04)	29s
Test (macos-latest)	37s
Test (macos-11)	1s
Test (beta)	30s
Test on Musl (ubuntu)	36s
Test (ubuntu-20.04)	31s
Test with Rust nightly (ubuntu)	29s
Test (aarch64-ubuntu)	2m 16s
Test with Rust nightly (windows)	1m 40s
	24m 42s

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