Don't use space btween if and condition in CMake files

[jjuhl]

Looking at what is the common style in CMake files reveals that one should not have a space between the 'if' and the actual condition. That clashes very much with what I personally prefer, but maintaining concistency is much more important. So, here's a commit that makes the style consistent.

[texus]

There are also CMakeLists.txt files in tests/, src/Backend and src/ where similar changes can be made.

You accidentally changed a line in examples/main-SFML_GRAPHICS.cpp, which isn't a cmake file.

[jjuhl]

Thank you for the feedback. I'll fix that up and update the PR.