Allow redeclaration of typedef yyscan_t

This is allowed in C11, so we don't need the workaround guards against
it anymore.  This effectively reverts commit 382092a0cd that put
these guards in place.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/10d32190-f31b-40a5-b177-11db55597355@eisentraut.org

contrib/cube/cubedata.h

@@ -62,10 +62,7 @@ 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

@@ -16,10 +16,7 @@ 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);

src/backend/utils/adt/jsonpath_internal.h

@@ -22,10 +22,7 @@ typedef struct JsonPathString
 	int			total;
 } JsonPathString;
 
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 
 #include "utils/jsonpath.h"
 #include "jsonpath_gram.h"

src/bin/pgbench/pgbench.h

@@ -20,10 +20,7 @@
  * here looking like the definitions in exprscan.l.  exprparse.y and
  * pgbench.c also use this to be able to declare things as "yyscan_t".
  */
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 
 /*
  * Likewise, we can't see exprparse.y's definition of union YYSTYPE here,

src/include/bootstrap/bootstrap.h

@@ -56,10 +56,7 @@ extern void boot_get_type_io_data(Oid typid,
 								  Oid *typoutput);
 
 union YYSTYPE;
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 
 extern int	boot_yyparse(yyscan_t yyscanner);
 extern int	boot_yylex_init(yyscan_t *yyscannerp);

src/include/fe_utils/psqlscan_int.h

@@ -51,14 +51,8 @@
  * validity checking; in actual use, this file should always be included
  * from the body of a flex file, where these symbols are already defined.
  */
-#ifndef YY_TYPEDEF_YY_BUFFER_STATE
-#define YY_TYPEDEF_YY_BUFFER_STATE
 typedef struct yy_buffer_state *YY_BUFFER_STATE;
-#endif
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 
 /*
  * We use a stack of flex buffers to handle substitution of psql variables.

src/include/replication/syncrep.h

@@ -97,10 +97,7 @@ extern void SyncRepUpdateSyncStandbysDefined(void);
  * in syncrep_gram.y and syncrep_scanner.l
  */
 union YYSTYPE;
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 extern int	syncrep_yyparse(SyncRepConfigData **syncrep_parse_result_p, char **syncrep_parse_error_msg_p, yyscan_t yyscanner);
 extern int	syncrep_yylex(union YYSTYPE *yylval_param, char **syncrep_parse_error_msg_p, yyscan_t yyscanner);
 extern void syncrep_yyerror(SyncRepConfigData **syncrep_parse_result_p, char **syncrep_parse_error_msg_p, yyscan_t yyscanner, const char *str);

src/include/replication/walsender_private.h

@@ -141,10 +141,7 @@ extern void WalSndSetState(WalSndState state);
  * repl_scanner.l
  */
 union YYSTYPE;
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 extern int	replication_yyparse(Node **replication_parse_result_p, yyscan_t yyscanner);
 extern int	replication_yylex(union YYSTYPE *yylval_param, yyscan_t yyscanner);
 pg_noreturn extern void replication_yyerror(Node **replication_parse_result_p, yyscan_t yyscanner, const char *message);

src/pl/plpgsql/src/plpgsql.h

@@ -1307,10 +1307,7 @@ extern void plpgsql_dumptree(PLpgSQL_function *func);
  */
 union YYSTYPE;
 #define YYLTYPE int
-#ifndef YY_TYPEDEF_YY_SCANNER_T
-#define YY_TYPEDEF_YY_SCANNER_T
 typedef void *yyscan_t;
-#endif
 extern int	plpgsql_yylex(union YYSTYPE *yylvalp, YYLTYPE *yyllocp, yyscan_t yyscanner);
 extern int	plpgsql_token_length(yyscan_t yyscanner);
 extern void plpgsql_push_back_token(int token, union YYSTYPE *yylvalp, YYLTYPE *yyllocp, yyscan_t yyscanner);