patch 8.0.1133: syntax timeout not used correctly

Problem:    Syntax timeout not used correctly.
Solution:   Do not pass the timeout to syntax_start() but set it explicitly.
            (Yasuhiro Matsumoto, closes #2139)
diff --git a/src/proto/syntax.pro b/src/proto/syntax.pro
index f6ecb8c..966a5cb 100644
--- a/src/proto/syntax.pro
+++ b/src/proto/syntax.pro
@@ -1,5 +1,6 @@
 /* syntax.c */
-void syntax_start(win_T *wp, linenr_T lnum, proftime_T *syntax_tm);
+void syn_set_timeout(proftime_T *tm);
+void syntax_start(win_T *wp, linenr_T lnum);
 void syn_stack_free_all(synblock_T *block);
 void syn_stack_apply_changes(buf_T *buf);
 void syntax_end_parsing(linenr_T lnum);