Bugfix: mysql-connector-cpp cmake files not work well when as a third party

[louishust]

When using mysql-connector-cpp as a third-party code in project like below:

project(XDEV-DEMO)

cmake_minimum_required(VERSION 3.0.2)

add_subdirectory(third_party/mysql-connector-cpp)
include_directories(third_party/mysql-connector-cpp/include)

add_executable(demo demo.cc)
target_link_libraries(demo connector)

mysql-connector-cpp will not compile correctly when as a submodule project.

[mysql-oca-bot]

Hi, thank you for submitting this pull request. In order to consider your code we need you to sign the Oracle Contribution Agreement (OCA). Please review the details and follow the instructions at http://www.oracle.com/technetwork/community/oca-486395.html
Please make sure to include your MySQL bug system user (email) in the returned form.
Thanks

[louishust]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[louishust]

@mysql-oca-bot I already mailed OCA yesterday, plz check it.

[mysql-admin]

@louishust It can take a few days ntil the contribution is entered into the system. Once done the contribution will be taken

Thanks for your contribution
==Omer

[mysql-oca-bot]

Hi, there was no response to our request to sign an OCA or confirm the code is submitted under the terms of the OCA. As such this request will be closed.
Thanks

[rsomla1]

Note: as of version 9.0+ this should be no longer an issue (the relevant cmake scripts have changed)