Allow -none- as an option for E3_DBDS

configure/TOP_RULES_REQUIRE

@@ -6,7 +6,7 @@ E3_SRC_PACKAGE_DIRS = $(wildcard $(addprefix $(INSTALL_LOCATION)/,$(E3_PACKAGE_D
 E3_DEST_PACKAGE_DIR = $(EPICS_MODULES)/$(E3_LIBRARY_NAME)/$(E3_LIBRARY_VERSION)
 GLOBAL_DBD = $(INSTALL_LOCATION)/dbd/e3-$(E3_LIBRARY_NAME).dbd
 
-E3_INCLUDE_DBDS = $(or $(strip $(E3_DBDS)),$(wildcard $(INSTALL_LOCATION)/dbd/*.dbd))
+E3_INCLUDE_DBDS = $(if $(E3_DBDS),$(filter-out -none-,$(E3_DBDS)),$(wildcard $(INSTALL_LOCATION)/dbd/*.dbd))
 
 define global_depfile
 package: $(INSTALL_LOCATION)/lib/$(1)/$(E3_LIBRARY_NAME).dep