Add -fopenmp, if present, to pkg-config file

The -fopenmp flag really needs to be propagated to all dependencies.
Original: 08cb4352d7ac88e116007b03fdac7e6b2fad39ed

lalinference/lalinference-uninstalled.pc.in

@@ -9,4 +9,4 @@ Description: (uninstalled)
 Version: @VERSION@
 Requires: gsl, lal >= @LAL_VERSION@, libmetaio, lalmetaio >= @LALMETAIO_VERSION@, lalinspiral >= @LALINSPIRAL_VERSION@, lalpulsar >= @LALPULSAR_VERSION@
 Libs: ${abs_top_builddir}/src/liblalinference.la
-Cflags: -I${abs_top_builddir}/include
+Cflags: -I${abs_top_builddir}/include @OPENMP_CFLAGS@

lalinference/lalinference.pc.in

@@ -12,4 +12,4 @@ Description: LAL Inference Library Support
 Version: @VERSION@
 Requires: gsl, lal >= @LAL_VERSION@, libmetaio, lalmetaio >= @LALMETAIO_VERSION@, lalinspiral >= @LALINSPIRAL_VERSION@, lalpulsar >= @LALPULSAR_VERSION@
 Libs: -L${libdir} -llalinference
-Cflags: -I${includedir}
+Cflags: -I${includedir} @OPENMP_CFLAGS@