Fix some issue that happen when I try to compile source at own enviroment.

Hi.

After reading your article http://habrahabr.ru/post/243011/ try to compile on self environment (On Ubuntu and Windows) but some issue happen during this process. So I present to you my fix of this problems.
I do not upload SDL2 and gtest for windows so it may be do manual (CMakeLists.txt expect that present at source folder).
Two major error happen: multiply definition of main - at test main file, that do not need as gtest have own
CMakeFiles/tests.dir/usr/src/gtest/src/gtest_main.cc.o: In function `main':
gtest_main.cc:(.text+0x0): multiple definition of `main'
CMakeFiles/tests.dir/tests/src/main.cpp.o:main.cpp:(.text+0x0): first defined here
And mingw32 have own make, so that do not need to link because on app side we have own.

Cheers!