enables arena based instruction sequence in hackc
Summary:
This diff enables arena based instruction sequence in hhvm and hhbc service lab experiment
- a flag, `-vRuntime.Eval.EnableHhbcByRef` , is introduced for choosing new `InstrSeq` vs old one in hhvm, the default value is `true`.
- hhbc service lab experiment is also switched to new implementation,
- in-proc hackc is also switched to new implementation.
Reviewed By: shayne-fletcher
Differential Revision:
D27351012
fbshipit-source-id:
7202f56a531ec2ac526bef3ea9bbaba9eb780796