Convert cgCountArray to SSA

Summary: Introduce unlikelyCond() for generating if/then/else blocks
where the "true" case is unlikely. Use it for cgCountArray().

Reviewed By: @alexmalyshev

Differential Revision: D1568375
Convert cgInstanceOf() and cgLdClsCtx() to SSA

Reviewed By: @alexmalyshev

Differential Revision: D1568392
convert cgConvDblToInt() and cgConvObjToBool to SSA

Reviewed By: @alexmalyshev

Differential Revision: D1568404