Don't filter OPENMP flags (-openmp & -fopenmp) from linker lines.

Don't filter OPENMP flags (-openmp & -fopenmp) from linker lines.

If -fopenmp if passed to gcc during linking, it will take care to add all
necessary libs to link correctly for openmp support. Currently libtool filters
those flags, similar as it was the case with the threading flags. This change
handles the situation for the openmp support similar as before the thread
support was fixed.

http://lists.gnu.org/archive/html/bug-libtool/2010-12/msg00009.html
http://lists.gnu.org/archive/html/bug-libtool/2011-03/msg00014.html

* libltdl/config/ltmain.m4sh (func_mode_link): Treat OpenMP
flags like pthreads flags.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>