Integrate RISC-V support #5

Job	Run time
build-native-gcc	3m 12s
build-native-llvm	5m 33s
test-native-gcc	13m 57s
build-aarch64-gcc	6m 48s
test-native-llvm	7m 11s
build-armhf-gcc	1m 11s
build-ppc64el-gcc	5m 29s
build-s390x-gcc	4m 50s
build-aarch64-llvm	4m 53s
build-armhf-llvm	5m 6s
build-riscv64-llvm	4m 24s
test-aarch64-gcc (qemu_cpu: "max,sve=off")	21m 51s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve128=on")	16m 59s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve256=on")	20m 47s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve512=on")	22m 30s
test-armhf-gcc (qemu_cpu: "max")	6m 14s
test-armhf-llvm (qemu_cpu: "max")	5m 38s
test-ppc64el-gcc (qemu_cpu: "power10")	34m 46s
test-s390x-gcc (qemu_cpu: "")	13m 25s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=false")	7m 2s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=128,elen=64,vext_spec=v1.0")	8m 23s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=256,elen=64,vext_spec=v1.0")	6m 27s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=512,elen=64,vext_spec=v1.0")	10m 9s
	3h 56m 45s

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