bison warnings on ubuntu 20.04 on deprecated directive in sql_yacc.yy

Generating sql_yacc.cc, sql_yacc.h

cd /tmp/es-build/build/sql && /usr/bin/bison -y -p MYSQL --output=/tmp/es-build/build/sql/sql_yacc.cc --defines=/tmp/es-build/build/sql/sql_yacc.h /tmp/es-build/sql/sql_yacc.yy

/tmp/es-build/sql/sql_yacc.yy:1021.1-12: warning: POSIX Yacc does not support %pure-parser [-Wyacc]

 1021 | %pure-parser                                    /* We have threads */

      | ^~~~~~~~~~~~

/tmp/es-build/sql/sql_yacc.yy:1021.1-12: warning: deprecated directive, use '%define api.pure' [-Wdeprecated]

 1021 | %pure-parser                                    /* We have threads */

      | ^~~~~~~~~~~~

/tmp/es-build/sql/sql_yacc.yy:1028.1-7: warning: POSIX Yacc does not support %expect [-Wyacc]

 1028 | %expect 101

      | ^~~~~~~

/tmp/es-build/sql/sql_yacc.yy: warning: fix-its can be applied.  Rerun with option '--update'. [-Wother]