Add better support for arrays and struct fields in IR.

Also add option for named registers.

examples/sysdialect_asm.janet

@@ -4,11 +4,12 @@
      (prim 1 f64)
      (struct 2 0 1)
      (pointer 3 0)
+     (array 4 1 1024)
      (bind 0 0)
      (bind 1 0)
      (bind 2 0)
      (bind 3 1)
-     (bind 4 1)
+     (bind bob 1)
      (bind 5 1)
      (bind 6 2)
      (constant 0 10)
@@ -17,10 +18,8 @@
      (add 2 1 0)
      (constant 3 1.77)
      (call 3 sin 3)
-     (cast 4 2)
-     (fset 2 6 0)
-     (fset 3 6 1)
-     (add 5 4 3)
+     (cast bob 2)
+     (add 5 bob 3)
      (jump :location)
      (return 5))
    :parameter-count 0