Support parallel builds with make #34

Job	Run time
build-native-gcc	3m 57s
build-native-llvm	4m 23s
test-native-gcc	8m 10s
build-aarch64-gcc	7m 46s
test-native-llvm	7m 18s
build-aarch64-llvm	2m 56s
build-armhf-gcc	4m 28s
build-armhf-llvm	1m 27s
build-ppc64el-gcc	2m 46s
build-ppc64el-llvm	3m 3s
build-s390x-gcc	5m 39s
build-s390x-llvm	2m 16s
build-riscv64-llvm	4m 16s
test-aarch64-gcc (qemu_cpu: "max,sve=off")	16m 35s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve128=on")	23m 30s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve256=on")	30m 4s
test-aarch64-gcc (qemu_cpu: "max,sve=on,sve512=on")	31m 8s
test-armhf-gcc (qemu_cpu: "max")	16m 8s
test-armhf-llvm (qemu_cpu: "max")	13m 36s
test-ppc64el-gcc (qemu_cpu: "power10")	26m 17s
test-ppc64el-llvm (qemu_cpu: "power10")	24m 33s
test-s390x-gcc (qemu_cpu: "")	19m 50s
test-s390x-llvm (qemu_cpu: "")	21m 36s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=false")	4m 13s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=128,elen=64,vext_spec=v1.0")	16m 40s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=256,elen=64,vext_spec=v1.0")	23m 1s
test-riscv64-llvm (qemu_cpu: "rv64,zba=true,zbb=true,zbs=true,v=true,vlen=512,elen=64,vext_spec=v1.0")	31m 25s
	5h 57m 1s

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