bc: unbreak FEATURE_CLEAN_UP build

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index df3c2d3..9e09700 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1786,7 +1786,7 @@
 	FOR_SHELL        = DO_HISTORY | TAB_COMPLETION | USERNAME_COMPLETION,
 };
 line_input_t *new_line_input_t(int flags) FAST_FUNC;
-/* So far static: void free_line_input_t(line_input_t *n) FAST_FUNC; */
+void free_line_input_t(line_input_t *n) FAST_FUNC;
 /*
  * maxsize must be >= 2.
  * Returns: