patch 8.1.1724: too much overhead checking for CTRL-C while processing text

Problem:    Too much overhead checking for CTRL-C while processing text.
Solution:   Increase BREAKCHECK_SKIP.  Remove the difference for when built
            with the GUI. (suggested by Andy Massimino, closes #4708)

src/feature.h

@@ -483,6 +483,11 @@
 # define FEAT_TEXT_PROP
 #endif
 
+#if defined(FEAT_SYN_HL) && defined(FEAT_RELTIME)
+// Can limit syntax highlight time to 'redrawtime'.
+# define SYN_TIME_LIMIT 1
+#endif
+
 /*
  * +spell		spell checking
  *