yyin has an odd redefinition error in scan.l, so we ensure that we don't
acidentally re-declare it.

diff --git flexdef.h flexdef.h
index 3eb710a..94ef024 100644
--- flexdef.h
+++ flexdef.h
@@ -421,7 +421,7 @@ extern int yymore_really_used, reject_really_used;
  */
 
 extern int datapos, dataline, linenum, out_linenum;
-extern FILE *skelfile, *yyin, *backing_up_file;
+extern FILE *skelfile, *backing_up_file;
 extern const char *skel[];
 extern int skel_ind;
 extern char *infilename, *outfilename, *headerfilename;
@@ -432,6 +432,10 @@ extern char **input_files;
 extern int num_input_files;
 extern char *program_name;
 
+#ifndef yyin_defined
+extern FILE* yyin;
+#endif
+
 extern char *action_array;
 extern int action_size;
 extern int defs1_offset, prolog_offset, action_offset, action_index;
--- scan.l
+++ scan.l
@@ -32,6 +32,7 @@
 /*  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR */
 /*  PURPOSE. */
 
+#define yyin_defined
 #include "flexdef.h"
 #include "parse.h"