patch 8.2.1255: cannot use a lambda with quickfix functions

Problem:    Cannot use a lambda with quickfix functions.
Solution:   Add support for lambda. (Yegappan Lakshmanan, closes #6499)
diff --git a/src/proto/quickfix.pro b/src/proto/quickfix.pro
index 0d84112..abe5b39 100644
--- a/src/proto/quickfix.pro
+++ b/src/proto/quickfix.pro
@@ -15,6 +15,7 @@
 void ex_copen(exarg_T *eap);
 void ex_cbottom(exarg_T *eap);
 linenr_T qf_current_entry(win_T *wp);
+int qf_process_qftf_option(void);
 int grep_internal(cmdidx_T cmdidx);
 void ex_make(exarg_T *eap);
 int qf_get_size(exarg_T *eap);