selfhost: structlookup/enumlookup mod-filter (mirror aliaslookup)

Tags structinfo/enumtype with originating module; exact-match first,
then split pkg.X and filter by smod/emod. Without this, two modules
with same-leaf-name struct/enum types collapsed to whichever entry
appeared first in the chain.

Wired into 696_modtype_leaf_collision via a wwstage run_pos using
ww_ww (negative case omitted: w6c_ww has no checkfile pass). Updated
the test's Makefile deps to include the wwstage binaries.

Audited the rest of the lookup family — fnretlookup, fnparamslookup,
deflookup don't need the same treatment: the parser emits N_DOT.str
(call/field name) as the leaf only, and fnparamslookup is only
invoked with N_IDENT.str. Dotted module-qualified function calls go
through the module-mangling path instead.

test/wcc/696_modtype_leaf_collision.c

@@ -97,6 +97,8 @@ main(void)
 
 	char cdrv[1024];
 	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);
+	char wdrv[1024];
+	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);
 
 	char fixdir[1024];
 	if (getcwd(fixdir, sizeof fixdir) == NULL) return 1;
@@ -108,12 +110,18 @@ main(void)
 	int fail = 0;
 	fail += run_pos(cdrv, fixdir, "cstage");
 	fail += run_neg(cdrv, fixdir, "cstage");
+	fail += run_pos(wdrv, fixdir, "wwstage");
+	/* No wwstage neg case: w6c_ww has no checkfile pass, so a
+	 * missing-field reference doesn't surface as a build error.
+	 * The positive case alone pins the structlookup mod-filter
+	 * (without it, `mod2.stream` would either fail to resolve or
+	 * silently bind to mod1.stream and miscompute the exit). */
 
 	if (fail) {
 		fprintf(stderr,
 		    "modtype_leaf_collision: %d case(s) failed\n", fail);
 		return 1;
 	}
-	printf("modtype_leaf_collision: 2/2 ok\n");
+	printf("modtype_leaf_collision: 3/3 ok\n");
 	return 0;
 }