Add sysir test suite stub

examples/sysir/hello.janet

@@ -0,0 +1,16 @@
+(use ./frontend)
+
+(defn-external printf:int [fmt:pointer])
+(defn-external exit:void [x:int])
+
+(defsys _start:void []
+  (printf "hello, world!\n")
+  (exit (the int 0))
+  (return))
+
+(defn main [& args]
+  (def [_ what] args)
+  (eprint "MODE: " what)
+  (case what
+    "c" (dumpc)
+    "x64" (dumpx64)))