Bugfix: \n does not represent a newline character on Mac

So, use a temporary @n@ and replace it by a newline at the end

configure

@@ -2779,7 +2779,7 @@ enable_defines() {
 
     for a in ${ADDONS}; do
         local addon_name="$(basename ${a})"
-        DEFINE_ENABLE_ADDONS="${DEFINE_ENABLE_ADDONS}\n#define ENABLE_${addon_name} 1"
+        DEFINE_ENABLE_ADDONS="${DEFINE_ENABLE_ADDONS}@n@#define ENABLE_${addon_name} 1"
     done
 }
 
@@ -3220,6 +3220,8 @@ sed -e "s|@FLEXIBLESUSY_VERSION@|$FLEXIBLESUSY_VERSION|" \
     -e "s|@DEFINE_ENABLE_LATTICE_SOLVER@|$DEFINE_ENABLE_LATTICE_SOLVER|" \
     -e "s|@DEFINE_ENABLE_SEMI_ANALYTIC_SOLVER@|$DEFINE_ENABLE_SEMI_ANALYTIC_SOLVER|" \
     -e "s|@DEFINE_ENABLE_ADDONS@|$DEFINE_ENABLE_ADDONS|"       \
+    -e 's|@n@|\
+|g' \
     < $CONFIGHDR_TMPL > $CONFIGHDR
 
 sed -e "s|@FLEXIBLESUSY_VERSION@|$FLEXIBLESUSY_VERSION|" \