Add GSL config to tests as well

tests/Makefile.am

@@ -15,9 +15,9 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 # Add the source directory and debug to CFLAGS
-AM_CFLAGS = -I$(top_srcdir)/src $(HDF5_CPPFLAGS)
+AM_CFLAGS = -I$(top_srcdir)/src $(HDF5_CPPFLAGS) $(GSL_INCS)
 
-AM_LDFLAGS = ../src/.libs/libswiftsim.a $(HDF5_LDFLAGS) $(HDF5_LIBS) $(FFTW_LIBS) $(GRACKLE_LIBS)
+AM_LDFLAGS = ../src/.libs/libswiftsim.a $(HDF5_LDFLAGS) $(HDF5_LIBS) $(FFTW_LIBS) $(GRACKLE_LIBS) $(GSL_LIBS)
 
 # List of programs and scripts to run in the test suite
 TESTS = testGreetings testMaths testReading.sh testSingle testKernel testSymmetry \