refactor: install clang tools on demand #604

Job	Run time
powerpc-unknown-linux-gnu	3m 51s
aarch64-unknown-linux-musl	3m 14s
x86_64-unknown-linux-gnu	1m 52s
armv7-unknown-linux-gnueabihf	3m 28s
powerpc64le-unknown-linux-gnu	3m 14s
s390x-unknown-linux-gnu	3m 42s
aarch64-apple-darwin	3m 8s
arm-unknown-linux-gnueabi	3m 16s
x86_64-unknown-linux-musl	3m 18s
aarch64-unknown-linux-gnu	3m 20s
x86_64-apple-darwin	2m 42s
x86_64-pc-windows-msvc	4m 10s
arm-unknown-linux-gnueabihf	3m 16s
aarch64-pc-windows-msvc	4m 31s
publish	0s
	47m 2s

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