patch 8.0.1768: SET_NO_HLSEARCH() used in a wrong way

Problem:    SET_NO_HLSEARCH() used in a wrong way.
Solution:   Make it a function. (suggested by Dominique Pelle,
            closes #2850)
diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index 0eace62..acd6b08 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -66,6 +66,7 @@
 char_u *get_behave_arg(expand_T *xp, int idx);
 char_u *get_messages_arg(expand_T *xp, int idx);
 char_u *get_mapclear_arg(expand_T *xp, int idx);
+void set_no_hlsearch(int flag);
 int get_pressedreturn(void);
 void set_pressedreturn(int val);
 /* vim: set ft=c : */