[Xorp-hackers] Serializing link jobs in SCons

[Bruce Simpson]

Google's Chromium offsoot is using SCons also:
    http://osdir.com/ml/chromium-reviews/2009-11/msg03622.html
... this patch forces the 'flock' command to be used to serialize a link 
job. It is Linux specific, a BSD port exists (BSD likes to call its own 
flock, lockf.)

It seems SCons has a SideEffect() builder syntax, we don't use this [yet]:-
    http://www.scons.org/wiki/SConsMethods/SideEffect

It looks as though SCons as implemented in the XORP tree is serializing 
tests, which is what we want; this may be because both the Program and 
Action builders refer to the same target.

P.S. An SVN trunk static build is regression test OK on my desktop 
machine as of now. I'm exploring how to fix 'scons check' for 'shared=true'.