llv8: fix `WasNeutered` check
llv8: fix `WasNeutered` check

The `kBitFieldOffset` was loaded conditionally, why it needs to be
computed for all versions of V8.

PR-URL: https://github.com/indutny/llnode/pull/31
Reviewed-By: Howard Hellyer <318e722a2f3c0517a913efd57bb582023357e5e6@uk.ibm.com>

rnchamberlain/llnode,hhellyer/llnode,hhellyer/llnode,rnchamberlain/llnode,rnchamberlain/llnode,rnchamberlain/llnode,hhellyer/llnode,hhellyer/llnode