out-of-tree build from source tarball wrongly copies sql/sql_yacc.cc from source even if sql_yacc.yy is newer

I have seen a couple of distros (Arch, Debian) having problems when patching
sql/sql_yacc.yy. The problem is that the build does not regenerate
sql/sql_yacc.cc with bison, instead it copies the stale sql_yacc.cc from the
source dir.

This occurs with out-of-tree build, not sure with in-tree build.

Probably this code in sql/CMakeLists.txt is responsible, it does not seem to
take into account that the .yy file may be newer:

# Handle out-of-source build from source package with possibly broken 

# bison. Copy bison output to from source to build directory, if not already 

# there

IF (NOT ${CMAKE_CURRENT_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_BINARY_DIR})

  IF(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/sql_yacc.cc)

    IF(NOT EXISTS ${CMAKE_CURRENT_BINARY_DIR}/sql_yacc.cc)

      CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/sql_yacc.cc 

        ${CMAKE_CURRENT_BINARY_DIR}/sql_yacc.cc COPYONLY)

      CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/sql_yacc.h

        ${CMAKE_CURRENT_BINARY_DIR}/sql_yacc.h COPYONLY)

    ENDIF()

  ENDIF()

ENDIF()

My suggestion would be to just remove that. If people do out-of-tree build,
they need to have bison installed, no big deal. Better than getting wrong code
generated due to changes to sql/sql_yacc.yy not getting picked up.