wcc: c-side mangles private decls; main exempt as entry-point convention

cmd/wcc/parse.c

@@ -1174,6 +1174,10 @@ parsefile(Parser *p)
 			advance(p);
 			continue;
 		}
+		/* Stamp the lex's current `// MODULE: foo` directive on the
+		 * decl. cgen uses it to mangle non-exported names so two
+		 * modules can each privately define `cstrlen`/`streq`/etc. */
+		if (d != NULL) d->module = p->l->module;
 		if (head == NULL) head = d;
 		else tail->next = d;
 		tail = d;