Optimize `metadata` calls on Linux. #1685

Job	Run time
Rustfmt	6s
Check Cross-Compilation on Windows (stable)	1m 47s
Check Cross-Compilation on Windows (beta)	1m 30s
Check Cross-Compilation on Rust nightly (nightly)	2m 2s
Check Cross-Compilation (stable)	1m 15s
Check Cross-Compilation on Rust nightly on Windows (nightly)	1m 38s
Check Cross-Compilation (beta)	1m 26s
Test (stable)	34s
Test linux-raw support (ubuntu)	31s
Test (windows-latest)	2m 16s
Test (msrv)	1m 8s
Test linux-raw support (ubuntu-20.04)	28s
Test on Musl (ubuntu)	37s
Test (windows-2019)	2m 50s
Test (macos-latest)	30s
Test with Rust nightly (ubuntu)	30s
Test (macos-11)	1s
Fuzz Targets	43s
Test with Rust nightly (windows)	1m 34s
Test (beta)	30s
Test (ubuntu-20.04)	31s
Test (aarch64-ubuntu)	2m 23s
	24m 50s

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