Support *-unknown-linux-gnu under `hermetic_cc_toolchain` #2

Job	Run time
Test wasm (wasm32-unknown-unknown)	21s
Clippy	14s
Test CUDA support	35s
Test build-std (aarch64-tvos)	2m 13s
Test build-std (aarch64-tvos-sim)	1m 49s
MSRV (ubuntu-latest)	2m 44s
Rustfmt	15s
Test build-std (x86_64-tvos)	1m 57s
semver-checks	2m 24s
MSRV (windows-latest)	3m 13s
MSRV (macos-latest)	3m 6s
Test (stable)	1m 20s
Test (beta)	1m 24s
Test (nightly)	1m 21s
Test (linux32)	1m 37s
Test (macos)	3m 28s
Test (aarch64-macos)	2m 10s
Test (aarch64-ios)	1m 26s
Test (win32)	2m 57s
Test (win64)	3m 6s
Test (mingw32)	3m 9s
Test (mingw64)	3m 2s
Test (windows-2019)	3m 10s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	2m 58s
Test (windows-clang, windows-2019, stable, x86_64-pc-windows-msvc, clang, clang++)	3m 37s
Test (windows-clang-cl, windows-2019, stable, x86_64-pc-windows-msvc, clang-cl, clang-cl)	3m 16s
	56m 52s

Provide feedback