Add a kernel ELF module and load it in a new process.

Don't yet jump to userspace.

zion/usr/crt0.s

@@ -0,0 +1,10 @@
+.text
+
+.global _start
+_start:
+  call main
+  call _exit
+
+_exit:
+  mov $1, %rdi
+  syscall

zion/usr/zcall.cpp

@@ -0,0 +1,13 @@
+#include "include/zcall.h"
+
+#include <stdint.h>
+
+uint64_t SysCall1(uint64_t number, const void* first) {
+  uint64_t return_code;
+  asm("syscall" : "=a"(return_code) : "D"(number), "S"(first) : "rcx", "r11");
+  return return_code;
+}
+
+uint64_t ZDebug(const char* message) {
+  return SysCall1(Z_DEBUG_PRINT, message);
+}