Re: (ITS#7969) LMDB: Globally shared fields of meta-data are not 'volatile'.

[h.b.furuseth@usit.uio.no]

__sync_synchronize() needs an #ifdef around it.
#ifdef __GNUC__, or something more general?

Not sure what to do for the #else.  We could mostly
avoid using mm_txnid when the lockfile is initialized
and use mti_txnid instead (e.g. in pick_meta).  And
penalize MDB_NOLOCK with some sync call in the #else.

-- 
Hallvard