if YY_NO_INPUT is defined, disable not only the declaration but also

the definition of yyinput(), avoids compiler warnings with newer gcc.
from Kurt J. Lidl per PR misc/41160, with a minor change to make it
generate paired #directives in the "-+", ie c++, case

usr.bin/lex/flex.skl

@@ -1,7 +1,7 @@
 /* A lexical scanner generated by flex */
 
 /* Scanner skeleton version:
- * $NetBSD: flex.skl,v 1.22 2005/08/08 01:28:08 christos Exp $
+ * $NetBSD: flex.skl,v 1.23 2009/04/20 16:01:17 drochner Exp $
  */
 
 #define FLEX_SCANNER
@@ -987,6 +987,7 @@ void yyFlexLexer::yyunput( int c, register char* yy_bp )
 
 
 %-
+#ifndef YY_NO_INPUT
 #ifdef __cplusplus
 static int yyinput()
 #else
@@ -1062,6 +1063,9 @@ int yyFlexLexer::yyinput()
 
 	return c;
 	}
+%-
+#endif /* ifndef YY_NO_INPUT */
+%*
 
 
 %-