patch 8.0.0643: when a pattern search is slow Vim becomes unusable

Problem:    When 'hlsearch' is set and matching with the last search pattern
            is very slow, Vim becomes unusable.  Cannot quit search by
            pressing CTRL-C.
Solution:   When the search times out set a flag and don't try again.  Check
            for timeout and CTRL-C in NFA loop that adds states.

src/quickfix.c

@@ -2415,7 +2415,7 @@ win_found:
 	    save_cursor = curwin->w_cursor;
 	    curwin->w_cursor.lnum = 0;
 	    if (!do_search(NULL, '/', qf_ptr->qf_pattern, (long)1,
-							   SEARCH_KEEP, NULL))
+						      SEARCH_KEEP, NULL, NULL))
 		curwin->w_cursor = save_cursor;
 	}
 
@@ -4237,7 +4237,7 @@ ex_vimgrep(exarg_T *eap)
 	    {
 		col = 0;
 		while (vim_regexec_multi(&regmatch, curwin, buf, lnum,
-							       col, NULL) > 0)
+							  col, NULL, NULL) > 0)
 		{
 		    /* Pass the buffer number so that it gets used even for a
 		     * dummy buffer, unless duplicate_name is set, then the