patch 9.0.0749: alloc/free of buffer for each quickfix entry is inefficient

Problem:    Alloc/free of buffer for each quickfix entry is inefficient.
Solution:   Use a shared grow array. (Yegappan Lakshmanan, closes #11365)
diff --git a/src/proto/quickfix.pro b/src/proto/quickfix.pro
index 904a60a..913c3c4 100644
--- a/src/proto/quickfix.pro
+++ b/src/proto/quickfix.pro
@@ -35,6 +35,7 @@
 int cexpr_core(exarg_T *eap, typval_T *tv);
 void ex_cexpr(exarg_T *eap);
 void ex_helpgrep(exarg_T *eap);
+void free_quickfix(void);
 void f_getloclist(typval_T *argvars, typval_T *rettv);
 void f_getqflist(typval_T *argvars, typval_T *rettv);
 void f_setloclist(typval_T *argvars, typval_T *rettv);