Integrate RISC-V support (#477) #22

Job	Run time
build-native-gcc	3m 14s
build-native-llvm	3m 41s
test-native-gcc	8m 40s
test-native-llvm	7m 16s
build-aarch64-gcc	6m 11s
build-aarch64-llvm	5m 7s
build-armhf-gcc	6m 57s
build-armhf-llvm	3m 47s
build-ppc64el-gcc	4m 53s
build-ppc64el-llvm	6m 20s
build-s390x-gcc	3m 53s
build-s390x-llvm	4m 12s
build-riscv64-llvm	7m 1s
test-aarch64-gcc (qemu_cpu: "max,sve=off")	20m 40s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve128=on")	21m 46s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve256=on")	25m 4s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve512=on")	32m 21s
test-armhf-gcc (qemu_cpu: "max")	14m 19s
test-armhf-llvm (qemu_cpu: "max")	13m 38s
test-ppc64el-gcc (qemu_cpu: "power10")	26m 16s
test-ppc64el-llvm (qemu_cpu: "power10")	23m 53s
test-s390x-gcc (qemu_cpu: "")	19m 18s
test-s390x-llvm (qemu_cpu: "")	18m 19s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=false")	4m 16s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=128,elen=64,vext_spec=v1.0")	16m 9s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=256,elen=64,vext_spec=v1.0")	19m 43s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=512,elen=64,vext_spec=v1.0")	34m 12s
	6h 1m 6s

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