refactor: install clang tools on demand #591

Job	Run time
armv7-unknown-linux-gnueabihf	3m 47s
powerpc-unknown-linux-gnu	3m 17s
aarch64-unknown-linux-musl	3m 32s
x86_64-unknown-linux-musl	3m 25s
aarch64-pc-windows-msvc	4m 3s
x86_64-pc-windows-msvc	4m 7s
aarch64-unknown-linux-gnu	3m 17s
arm-unknown-linux-gnueabi	3m 19s
x86_64-apple-darwin	3m 2s
x86_64-unknown-linux-gnu	1m 53s
aarch64-apple-darwin	2m 28s
s390x-unknown-linux-gnu	3m 22s
powerpc64le-unknown-linux-gnu	3m 22s
arm-unknown-linux-gnueabihf	3m 29s
publish	0s
	46m 23s

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