www/libxul fails to upgrade if devel/libunwind is installed

[Torfinn Ingolfsen]

If devel/libunwind is installed, a portupgrade of www/libxul fails with:
nsStackWalk.cpp: In function 'nsresult NS_StackWalk(void (*)(void*,
void*), PRUint32, void*)':
nsStackWalk.cpp:1544: error: '_Unwind_Backtrace' was not declared in this scope
gmake[4]: *** [nsStackWalk.o] Error 1
gmake[4]: *** Waiting for unfinished jobs....
gmake[4]: Leaving directory
`/usr/ports/www/libxul/work/mozilla-1.9.2/xpcom/base'
gmake[3]: *** [libs] Error 2
gmake[3]: Leaving directory `/usr/ports/www/libxul/work/mozilla-1.9.2/xpcom'
gmake[2]: *** [libs_tier_xpcom] Error 2
gmake[2]: Leaving directory `/usr/ports/www/libxul/work/mozilla-1.9.2'
gmake[1]: *** [tier_xpcom] Error 2
gmake[1]: Leaving directory `/usr/ports/www/libxul/work/mozilla-1.9.2'
gmake: *** [default] Error 2
*** Error code 1

Stop in /usr/ports/www/libxul.
*** Error code 1

Stop in /usr/ports/www/libxul.

Simply deinstall  libunwind (it is required by blender), and libxul
upgrades without problem.

Has anyone else seen this?
I first became aware of this through this thread[1]  on the forums.

References:
1) http://forums.freebsd.org/showthread.php?p=183072
-- 
Regards,
Torfinn Ingolfsen