Makefile: Remove generator modules from the exclude list

There's no real reason to exclude 'generator' from the build or check
targets.  Add it back in.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Makefile

@@ -19,7 +19,7 @@ ALL_INFOS := $(INFO_SRCS:%_info=%info)
 ALL_MODULES := $(ALL_INFOS:%/info=%)
 
 # ... Except stuff that needs external dependencies, which we exclude
-EXCLUDE := altstack generator jmap jset nfs ogg_to_pcm tal/talloc wwviaudio
+EXCLUDE := altstack jmap jset nfs ogg_to_pcm tal/talloc wwviaudio
 MODULES:= $(filter-out $(EXCLUDE:%=ccan/%), $(ALL_MODULES))
 
 # Sources are C files in each module, objects the resulting .o files