Fix test 421-large-frame.

- Don't force the optimizing compiler to compile a huge
  method by reducing the number of local variables and
  instructions in Main.$opt$LargeFrame.
- Prevent the optimizing compiler from "optimizing too much"
  (through constant folding and inlining), so as to preserve
  a large stack frame in Main.$opt$LargeFrame.
- Keep the original huge method (without the $opt$ marker)
  as Main.HugeFrame.

Bug: 20020727
Change-Id: I49bf8f03146020bd94bd392684e605d7bb6daf1e