Add CMake toolchains #89

Job	Run time
Native build	18s
Cross build (alpha-unknown-linux-gnu)	5m 14s
Cross build (x86_64-unknown-linux-gnu)	5m 12s
Cross build (i386-unknown-linux-gnu)	5m 10s
Cross build (arm-unknown-linux-gnueabihf)	5m 14s
Cross build (hppa-unknown-linux-gnu)	5m 7s
Cross build (aarch64-unknown-linux-gnu)	5m 12s
Cross build (mips-unknown-linux-gnu)	4m 51s
Cross build (mipsel-unknown-linux-gnu)	4m 55s
Cross build (powerpc-unknown-linux-gnu)	5m 11s
Cross build (s390-unknown-linux-gnu)	5m 9s
Cross build (s390x-unknown-linux-gnu)	5m 13s
Cross build (sparc-unknown-linux-gnu)	5m 10s
Cross build (powerpc64le-unknown-linux-gnu)	5m 12s
	1h 7m 8s

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