Pull Request: Correct compatibility of the preprocessor value generated by Projucer and CMake

Hi, JUCE team.

I sent a PullRequest to your GitHub with the following content:

I have found incompatible behaviour between Projucer and CMake.
This issue causes problems when a project that was being developed using Projucer moves to using CMake.

Thanks for the patch and detailed explanation. The issue should be fixed by this commit: