Adds --with-driver option to configure

- Following suggestion from @marshallward I've implemented an option
  to select the driver code at the configure stage  (changes to
  configure.ac)
- This allows the target build/coupled/ocean_model_MOM.o to be built
  using the .testing ac tools.

.testing/Makefile

@@ -226,15 +226,19 @@ build/asymmetric/Makefile: MOM_ENV=$(PATH_FMS) $(ASYMMETRIC_FCFLAGS) $(MOM_LDFLA
 build/repro/Makefile: MOM_ENV=$(PATH_FMS) $(REPRO_FCFLAGS) $(MOM_LDFLAGS)
 build/openmp/Makefile: MOM_ENV=$(PATH_FMS) $(OPENMP_FCFLAGS) $(MOM_LDFLAGS)
 build/target/Makefile: MOM_ENV=$(PATH_FMS) $(TARGET_FCFLAGS) $(MOM_LDFLAGS)
-
+build/coupled/Makefile: MOM_ENV=$(PATH_FMS) $(SYMMETRIC_FCFLAGS) $(SYMMETRIC_LDFLAGS)
+build/nuopc/Makefile: MOM_ENV=$(PATH_FMS) $(SYMMETRIC_FCFLAGS) $(SYMMETRIC_LDFLAGS)
+build/mct/Makefile: MOM_ENV=$(PATH_FMS) $(SYMMETRIC_FCFLAGS) $(SYMMETRIC_LDFLAGS)
 
 # Configure script flags
 build/symmetric/Makefile: MOM_ACFLAGS=
 build/asymmetric/Makefile: MOM_ACFLAGS=--enable-asymmetric
 build/repro/Makefile: MOM_ACFLAGS=
 build/openmp/Makefile: MOM_ACFLAGS=--enable-openmp
 build/target/Makefile: MOM_ACFLAGS=
-
+build/coupled/Makefile: MOM_ACFLAGS=--with-driver=coupled_driver
+build/nuopc/Makefile: MOM_ACFLAGS=--with-driver=nuopc_driver
+build/mct/Makefile: MOM_ACFLAGS=--with-driver=mct_driver
 
 # Fetch regression target source code
 build/target/Makefile: | $(TARGET_CODEBASE)
@@ -336,29 +340,14 @@ $(DEPS)/Makefile: ../ac/deps/Makefile
 # - use autoconf rather than mkmf templates
 MK_TEMPLATE ?= ../../$(DEPS)/mkmf/templates/ncrc-gnu.mk
 # NUOPC driver
-build/nuopc/Makefile: ../config_src/nuopc_driver $(MOM_SOURCE)
-	mkdir -p $(@D)
-	cd $(@D) \
-	  && $(MOM_ENV) ../../$(DEPS)/mkmf/bin/list_paths -l ../../$(DEPS)/fms/src ../../../config_src/nuopc_driver ../../../config_src/dynamic_symmetric ../../../src/ ../../../config_src/external \
-	  && $(MOM_ENV) ../../$(DEPS)/mkmf/bin/mkmf -t $(MK_TEMPLATE) -p MOM6 path_names
 build/nuopc/mom_ocean_model_nuopc.o: build/nuopc/Makefile
 	cd $(@D) && make $(@F)
 check_mom6_api_nuopc: build/nuopc/mom_ocean_model_nuopc.o
 # GFDL coupled driver
-build/coupled/Makefile: ../config_src/coupled_driver $(MOM_SOURCE)
-	mkdir -p $(@D)
-	cd $(@D) \
-	  && $(MOM_ENV) ../../$(DEPS)/mkmf/bin/list_paths -l ../../$(DEPS)/fms/src ../../../config_src/coupled_driver ../../../config_src/dynamic_symmetric ../../../src/ ../../../config_src/external \
-	  && $(MOM_ENV) ../../$(DEPS)/mkmf/bin/mkmf -t $(MK_TEMPLATE) -p MOM6 path_names
 build/coupled/ocean_model_MOM.o: build/coupled/Makefile
 	cd $(@D) && make $(@F)
 check_mom6_api_coupled: build/coupled/ocean_model_MOM.o
 # MCT driver
-build/mct/Makefile: ../config_src/mct_driver $(MOM_SOURCE)
-	mkdir -p $(@D)
-	cd $(@D) \
-	  && $(MOM_ENV) ../../$(DEPS)/mkmf/bin/list_paths -l ../../$(DEPS)/fms/src ../../../config_src/mct_driver ../../../config_src/dynamic_symmetric ../../../src/ ../../../config_src/external \
-	  && $(MOM_ENV) ../../$(DEPS)/mkmf/bin/mkmf -t $(MK_TEMPLATE) -p MOM6 path_names
 build/mct/mom_ocean_model_mct.o: build/mct/Makefile
 	cd $(@D) && make $(@F)
 check_mom6_api_mct: build/mct/mom_ocean_model_mct.o

ac/configure.ac

@@ -48,6 +48,12 @@ AC_ARG_ENABLE([asymmetric],
 AS_IF([test "$enable_asymmetric" = yes],
   [MEM_LAYOUT=${srcdir}/config_src/dynamic])
 
+# Default to solo_driver
+DRIVER_DIR=${srcdir}/config_src/solo_driver
+AC_ARG_WITH([driver],
+  AS_HELP_STRING([--with-driver=coupled_driver|solo_driver], [Select directory for driver source code]))
+AS_IF([test "x$with_driver" != "x"],
+  [DRIVER_DIR=${srcdir}/config_src/${with_driver}])
 
 # TODO: Rather than point to a pre-configured header file, autoconf could be
 # used to configure a header based on a template.
@@ -210,10 +216,10 @@ AS_IF([test -z "$MKMF"], [
 AC_CONFIG_COMMANDS([path_names],
   [list_paths -l \
     ${srcdir}/src \
-    ${srcdir}/config_src/solo_driver \
     ${srcdir}/config_src/ext* \
+    ${DRIVER_DIR} \
     ${MEM_LAYOUT}
-], [MEM_LAYOUT=$MEM_LAYOUT])
+], [MEM_LAYOUT=$MEM_LAYOUT DRIVER_DIR=$DRIVER_DIR])
 
 
 AC_CONFIG_COMMANDS([Makefile.mkmf],