lex files fail compilation under GCC 15 / C23 standard

[nuclearpidgeon]

In my continuing series of issues building Fluentbit under GCC 15: some errors have come out of the parts of the build that make use of flex and .l lexer definition files - specifically:

• The SQL parser in processor_sql (make -f CMakeFiles/Makefile2 plugins/processor_sql/parser/all)
• The record-accessor syntax parser in src/record_accessor (make -f CMakeFiles/Makefile2 src/record_accessor/all)
• The stream processor syntax parser (make -f CMakeFiles/Makefile2 src/stream_processor/parser/all)

Example build failure:

Building C object plugins/processor_sql/parser/CMakeFiles/processor-sql-parser.dir/processor-sql_parser.c.o
sql-parser.y:22:12: error: conflicting types for ‘yylex’; have ‘int(void)’
In file included from sql-parser.y:16:
/home/stewart/Projects/OSS/fluentbit-4/build/plugins/processor_sql/parser/processor-sql-parser_lex.h:338:12: note: previous declaration of ‘yylex’ with type ‘int(YYSTYPE *, void *)’
  338 | 
      |            ^    
/home/stewart/Projects/OSS/fluentbit-4/build/plugins/processor_sql/parser/processor-sql_parser.c: In function ‘yyparse’:
/home/stewart/Projects/OSS/fluentbit-4/build/plugins/processor_sql/parser/processor-sql_parser.c:1092:16: error: too many arguments to function ‘yylex’; expected 0, have 2
 1092 |       yychar = yylex (&yylval, scanner);
      |                ^~~~~  ~~~~~~~
sql-parser.y:22:12: note: declared here
make[1]: *** [plugins/processor_sql/parser/CMakeFiles/processor-sql-parser.dir/build.make:138: plugins/processor_sql/parser/CMakeFiles/processor-sql-parser.dir/processor-sql_parser.c.o] Error 1
make[1]: Leaving directory '/home/stewart/Projects/OSS/fluentbit-4/build'
make: *** [CMakeFiles/Makefile2:9308: plugins/processor_sql/parser/CMakeFiles/processor-sql-parser.dir/all] Error 2

When looking at the intermediary-generated build/plugins/processor_sql/parser/processor-sql_parser.c file in my IDE I see this declaration with a squiggly line under it:

extern int yylex();

...with this message:

A function declaration without a prototype is deprecated in all versions of C and is treated as a zero-parameter prototype in C23, conflicting with a previous declaration clang(-Wdeprecated-non-prototype)
processor-sql-parser_lex.h(339, 12): Conflicting prototype is here

build/plugins/processor_sql/parser/processor-sql-parser_lex.h at that line shows:

extern int yylex \
               (YYSTYPE * yylval_param , yyscan_t yyscanner);

It seems this stems from the extern int yylex(); declarations used in the .y files e.g.

fluent-bit/plugins/processor_sql/parser/sql-parser.y

Line 22 in 067c064

extern int yylex();

[cosmo0920]

This should be done by #10551.