Added preprocessor directives for specific compilers

[Sqeaky]

Added individual preprocessor macros for 4 msvc compiler, Clang, GCC and MinGw.

I also added a test function, TestPrepoc to the Process tests. This emits all the compiler macros and requests the user/tester visually inspect the result.

This is still from the same fork I made earlier. I think it ought to work seamlessly, but I have not attempted two requests from a single fork before.

[memsharded]

I am using @Sqeaky fork for creation of conan.io package (https://github.com/memsharded/conan-robot, https://www.conan.io/source/Robot/2.0/memsharded/testing), because it is more convenient having a CMakeLists.txt. So far, only tested VS14 and VS12, both static and shared linking, works great.