On Wednesday 15 May 2013 15:22:21 Michał Górny wrote:
> The 'userland_*' flags have proven not good enough to determine
> the availability of lock helpers. Fabian provided a nice portable
> locking code instead.
> 
> Fixes: https://bugs.gentoo.org/show_bug.cgi?id=466554
> ---
>  gx86/eclass/multibuild.eclass | 29 +++++++++++++++--------------

this seems more appropriate for portability.eclass than other random places.  
there you can keep flock when it's available, or fall back to manual hacks like 
this.
-mike