Support `-Zbuild-std` #689

Job	Run time
check rustfmt	7s
check clippy	21s
build-std (ubuntu-latest, x86_64-unknown-linux-gnu)	1m 46s
tests (ubuntu-latest, x86_64-unknown-linux-gnu)	3m 40s
build-std (macos-latest, x86_64-apple-darwin)	1m 51s
tests (macos-latest, x86_64-apple-darwin)	3m 32s
build-std (windows-latest, i686-pc-windows-msvc)	3m 5s
tests (windows-latest, i686-pc-windows-msvc)	7m 6s
	21m 28s

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