Cmake linux mac fixes

This should fix 3 issue with my [previous path](https://github.com/cocos2d/cocos2d-x/pull/9177#issuecomment-64158259) for cmake build system.

* Compile errors in MacOS X 10.8 (yes too old, but [forum post](http://discuss.cocos2d-x.org/t/cmake-for-mac-qtcreator-and-clion/16889/87) show that exists people that use it)
* Link with static libraries determined with `pkg-config --static --libs` not works on almost any Linux distros. So do not try to do it ever. (Someone who needs fully static build on linux, can improve prebuilt libs in external).
* FindFontconfig.cmake failed to find library on centos, because check FONTCONFIG_INCLUDE_DIRS, but on centos `pkg-config` returns empty include dirs, because package in standard search location for compiler.

All this fixed now. And tested, but not against current state. Because after commit: [Merge pull request #9193 from pipu/v3_flatbuffers](https://github.com/cocos2d/cocos2d-x/commit/fa22b126285674e3e0d0f2d5f2f39c56987b483e) build fully broken as folder external not contains source code for flatbuffers (