Add -DDBUG_ON to CXXFLAGS whenever it is added to CFLAGS.
  Thus, sql/ha_innodb.cc will be compiled with the same
  setting of UNIV_DEBUG as the rest of InnoDB,
  i.e., --with-debug enables InnoDB ut_ad() assertions
  everywhere.


configure.in:
  Add -DDBUG_ON to CXXFLAGS whenever it is added to CFLAGS.
  Thus, sql/ha_innodb.cc will be compiled with the same
  setting of UNIV_DEBUG as the rest of InnoDB,
  i.e., --with-debug enables InnoDB ut_ad() assertions
  everywhere.