MDEV-4267 : do not copy sql_yacc.cc and sql_yacc.h from unpacked source...

MDEV-4267 : do not copy sql_yacc.cc and sql_yacc.h from unpacked source tarball into build directory, if usable bison is installed on the build machine.

This is done in order to avoid possibly stale bison output files in the build directory.

sql/CMakeLists.txt

@@ -185,9 +185,12 @@ INSTALL_DEBUG_TARGET(mysqld
   PDB_DESTINATION ${INSTALL_SBINDIR}/debug
   RENAME mysqld-debug)
 
+INCLUDE(${CMAKE_SOURCE_DIR}/cmake/bison.cmake)
+
 # 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 BISON_USABLE)
 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)
@@ -198,9 +201,8 @@ IF (NOT ${CMAKE_CURRENT_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_BINARY_DIR})
     ENDIF()
   ENDIF()
 ENDIF()
+ENDIF()
 
-
-INCLUDE(${CMAKE_SOURCE_DIR}/cmake/bison.cmake)
 RUN_BISON(
   ${CMAKE_CURRENT_SOURCE_DIR}/sql_yacc.yy 
   ${CMAKE_CURRENT_BINARY_DIR}/sql_yacc.cc