Prevent redeclaration of typedef yyscan_t

Fix for 1f0de66: We need to prevent redeclaration of typedef
yyscan_t.  (This will work with C11 but not currently with C99.)  The
generated scanner files provide their own typedef, but we also need to
provide one for the interfaces that we expose.  So we need to add some
preprocessor guards to avoid a redefinition.  (This is how the
generated scanner files do it internally as well.)  This way
everything now works independent of the order in which things are
included.

Discussion: https://www.postgresql.org/message-id/flat/eb6faeac-2a8a-4b69-9189-c33c520e5b7b@eisentraut.org

Author: petere

contrib/cube/cubedata.h

@@ -62,7 +62,10 @@ typedef struct NDBOX
 /* for cubescan.l and cubeparse.y */
 /* All grammar constructs return strings */
 #define YYSTYPE char *
+#ifndef YY_TYPEDEF_YY_SCANNER_T
+#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
+#endif
 
 /* in cubescan.l */
 extern int	cube_yylex(YYSTYPE *yylval_param, yyscan_t yyscanner);

contrib/seg/segdata.h

@@ -16,7 +16,10 @@ extern int	significant_digits(const char *s);
 
 /* for segscan.l and segparse.y */
 union YYSTYPE;
+#ifndef YY_TYPEDEF_YY_SCANNER_T
+#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
+#endif
 
 /* in segscan.l */
 extern int	seg_yylex(union YYSTYPE *yylval_param, yyscan_t yyscanner);