[legal] Ignore config/local header files for licensing purposes

The config/local/*.h files are expected to be empty in most cases.
This should not cause a licence determination to fail.

Fix by ignoring config/local/*.h for licensing purposes.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/Makefile.housekeeping

 
 # Get licensing verdict for the specified target
 #
+define licensable_deps_list
+	$(filter-out config/local/%.h,$(call deps_list,$(1)))
+endef
 define unlicensed_deps_list
-	$(shell grep -L FILE_LICENCE $(call deps_list,$(1)))
+	$(shell grep -L FILE_LICENCE $(call licensable_deps_list,$(1)))
 endef
 define licence_list
 	$(patsubst __licence_%,%,\