linking pbnjson_cpp library for C++ wrappers

:Release Notes:

:Detailed Notes:
- moved pkg-config search from tests to upper make

:Testing Performed:
Desktop build

:QA Notes:

:Issues Addressed:
[BHV-5363] Create a separate shared library for C++ wrapper

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: If54f87b0a6439f0eb06ad0b9ce14ce0efd6802e3
Reviewed-on: https://g2g.palm.com/5596
Reviewed-by: DCO Verification
Reviewed-by: Andrii Zora <andrii.zora@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Sergiy Kryvonos <sergiy.kryvonos@lge.com>
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>