Replace jumbo opcodes in certain circumstances

Replace jumbo opcodes in certain circumstances

With this change we will start using some dexopt-generated "jumbo"
opcodes for volatile field accesses and calls to Object.<init>.  These
are necessary for correctness.

Fixed a bug that could prevent volatile fields in huge objects from
being handled correctly.

Also, return "void" from some functions whose return value is never
examined.

Change-Id: I2a7fc66b59953ed3a6f4ac507873101de5d101d5