ci: builds a test with -fimplicit-none -fmodule-private

.gitlab-ci.yml

@@ -376,7 +376,7 @@ test_levante_gcc:
     - .check_warnings
   variables:
     CFLAGS: -O0 -g -Wall -fsignaling-nans
-    FCFLAGS: -O0 -g -Wall -ffpe-trap=invalid -fcheck=bounds
+    FCFLAGS: -O0 -g -Wall -ffpe-trap=invalid -fcheck=bounds -fimplicit-none -fmodule-private
   script:
     - split_mpi_wrapper_command $CC
     - export CC=$smwc_CC; export MPI_CFLAGS=$smwc_CFLAGS; export MPI_CLIBS=$smwc_LDFLAGS