Add ffi jit example.

examples/jitfn/hello.nasm

@@ -0,0 +1,17 @@
+BITS 64
+
+;;;
+;;; Code
+;;;
+mov rax, 1          ; write(
+mov rdi, 1          ;   STDOUT_FILENO,
+lea rsi, [rel msg]  ;   msg,
+mov rdx, msglen     ;   sizeof(msg)
+syscall             ; );
+ret                 ; return;
+
+;;;
+;;; Constants
+;;;
+msg: db "Hello, world!", 10
+msglen: equ $ - msg