MDEV-21286: bison warnings on ubuntu 20.04 on deprecated directive in sql_yacc.yy

Results with
```
%define api.pure                                    /* We have threads */
```
in `<build-dir>/sql/[yy_mariadb|yy_oracle].yy` files.

Reviewed by: wlad@mariadb.com

sql/CMakeLists.txt

@@ -65,6 +65,8 @@ ADD_CUSTOM_COMMAND(
   DEPENDS gen_lex_token
 )
 
+FIND_PACKAGE(BISON 2.0)
+
 ADD_CUSTOM_COMMAND(
   OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/yy_mariadb.yy
          ${CMAKE_CURRENT_BINARY_DIR}/yy_oracle.yy
@@ -72,6 +74,7 @@ ADD_CUSTOM_COMMAND(
    "-DOUT1=${CMAKE_CURRENT_BINARY_DIR}/yy_oracle.yy"
    "-DOUT2=${CMAKE_CURRENT_BINARY_DIR}/yy_mariadb.yy"
    "-DIN=${CMAKE_CURRENT_SOURCE_DIR}/sql_yacc.yy"
+    "-DBISON_VERSION=${BISON_VERSION}"
    -P ${CMAKE_CURRENT_SOURCE_DIR}/gen_yy_files.cmake
   COMMENT "Building yy_mariadb.yy and yy_oracle.yy from sql_yacc.yy"
   DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/sql_yacc.yy
@@ -321,8 +324,6 @@ IF(WITH_MYSQLD_LDFLAGS)
 ENDIF()
 
 
-FIND_PACKAGE(BISON 2.0)
-
 
 # Handle out-of-source build from source package with possibly broken 
 # bison. Copy bison output to from source to build directory, if not already 

sql/gen_yy_files.cmake

@@ -5,6 +5,9 @@ file(READ "${IN}" data)
 file(WRITE "${OUT1}" "")
 file(WRITE "${OUT2}" "")
 set(where 0)
+if(NOT(BISON_VERSION VERSION_LESS "3.0.0"))
+  string(REPLACE "\n%pure-parser" "\n%define api.pure" data "${data}")
+endif()
 string(REGEX REPLACE "/\\* sql_yacc\\.yy \\*/" "/* DON'T EDIT THIS FILE. IT'S GENERATED.  EDIT sql_yacc.yy INSTEAD */" data "${data}")
 while(NOT data STREQUAL "")
   string(REGEX MATCH "^(%[ie][^\n]*\n)|((%[^ie\n]|[^%\n])[^\n]*\n)+|\n+" line "${data}")