Support `@host` vars. #379

Job	Run time
host=ubuntu-22.04 cmd=cli target=x86_64-linux-gnu mode=release	3m 1s
host=ubuntu-22.04 cmd=cli target=x86_64-selinux-gnu mode=release	2m 24s
host=macos-12 cmd=cli target=x86_64-macos-none mode=release	2m 19s
host=macos-12 cmd=cli target=aarch64-macos-none mode=release	3m 31s
host=windows-2022 cmd=cli target=x86_64-windows-gnu mode=release	4m 41s
host=windows-2022 cmd=lib target=x86_64-windows-gnu mode=release	4m 12s
host=ubuntu-22.04 cmd=lib target=wasm32-freestanding mode=release	1m 49s
host=ubuntu-22.04 cmd=lib target=x86_64-linux-gnu mode=release	2m 5s
host=macos-12 cmd=lib target=x86_64-macos-none mode=release	2m 55s
host=macos-12 cmd=lib target=aarch64-macos-none mode=release	1m 52s
Release	17s
	29m 6s

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