build: add a "user" arch to allow the kernel to run as a program on the host machine

arch/user/cpu.c

@@ -0,0 +1,24 @@
+#include <unistd.h>
+#include <socks/machine/cpu.h>
+
+int ml_init_bootcpu(void)
+{
+	return 0;
+}
+
+int ml_cpu_block_init(ml_cpu_block *p)
+{
+	return 0;
+}
+
+int ml_cpu_block_use(ml_cpu_block *p)
+{
+	return 0;
+}
+
+void ml_halt_cpu(void)
+{
+	while (1) {
+		sleep(100);
+	}
+}