sys: add MIPS R6 support (#2138) #47

Job	Run time
macos	1m 33s
minver	18s
rust_stable	1m 38s
linux_native_builds (x86_64-unknown-linux-gnu)	1m 3s
rustfmt	4s
linux_native_builds (x86_64-unknown-linux-musl)	1m 28s
tier3 (x86_64-unknown-dragonfly)	1m 20s
tier3 (x86_64-unknown-openbsd)	50s
tier3 (armv7-unknown-linux-uclibceabihf)	1m 13s
tier3 (x86_64-unknown-haiku)	1m 15s
redox	44s
cross (arm-unknown-linux-gnueabi)	2m 26s
cross_compiling (aarch64-linux-android)	33s
cross (armv7-unknown-linux-gnueabihf)	2m 18s
cross_compiling (arm-linux-androideabi)	44s
cross (i686-unknown-linux-gnu)	2m 46s
cross_compiling (armv7-linux-androideabi)	30s
cross (i686-unknown-linux-musl)	2m 22s
cross_compiling (i686-linux-android)	41s
cross (mips-unknown-linux-gnu)	2m 9s
cross_compiling (x86_64-linux-android)	53s
cross (mips64-unknown-linux-gnuabi64)	1m 40s
cross_compiling (arm-unknown-linux-musleabi)	54s
cross (mips64el-unknown-linux-gnuabi64)	1m 31s
cross_compiling (x86_64-unknown-fuchsia)	24s
cross (mipsel-unknown-linux-gnu)	2m 38s
cross_compiling (x86_64-unknown-illumos)	25s
cross (powerpc64le-unknown-linux-gnu)	2m 19s
cross_compiling (aarch64-apple-ios, true)	33s
cross_compiling (powerpc64-unknown-linux-gnu)	42s
cross_compiling (s390x-unknown-linux-gnu)	34s
cross_compiling (x86_64-unknown-linux-gnux32)	30s
cross_compiling (x86_64-unknown-netbsd)	50s
	39m 48s

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