Add CMake toolchains #91

Job	Run time
Native build	19s
Cross build (alpha-unknown-linux-gnu)	3m 29s
Cross build (x86_64-unknown-linux-gnu)	44m 21s
Cross build (i386-unknown-linux-gnu)	44m 24s
Cross build (arm-unknown-linux-gnueabi)	5m 2s
Cross build (arm-unknown-linux-gnueabihf)	8m 50s
Cross build (hppa-unknown-linux-gnu)	3m 44s
Cross build (aarch64-unknown-linux-gnu)	9m 45s
Cross build (mips-unknown-linux-gnu)	4m 56s
Cross build (mipsel-unknown-linux-gnu)	4m 57s
Cross build (powerpc-unknown-linux-gnu)	8m 55s
Cross build (s390-unknown-linux-gnu)	3m 42s
Cross build (s390x-unknown-linux-gnu)	8m 55s
Cross build (sparc-unknown-linux-gnu)	8m 39s
Cross build (powerpc64le-unknown-linux-gnu)	9m 10s
	2h 49m 8s

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