Fix run-test 458-long-to-fpu.

- Make $noinline$DoubleConvert actually exercise
  long-to-double conversions (instead of long-to-float
  conversions).
- Change the inlining-defeating strategy: introduce an
  always-throwing branch in $noinline$FloatConvert and
  $noinline$DoubleConvert instead of using recursion, as the
  inliner now inlines recursive calls (down to a certain
  depth).

Change-Id: Ib83a89039968e597cf74d26b5779d410f3caf743