[CMake] Removing unused configuration types for Xcode

[Claus Höfele]

Hi all,

I have the following lines in my top-level CMakeLists.txt to get rid
of all configuration types except for Debug and Release:

cmake_minimum_required(VERSION 2.6)
set(CMAKE_CONFIGURATION_TYPES Debug Release CACHE TYPE INTERNAL FORCE)
project(2dots)
# ...

That works when generating project files for Visual Studio, but
MinSizeRel and RelWithDebInfo still turn up in Xcode.

Is this a bug or do I have to reorder the commands somehow? I remember
that I had to set CMAKE_CONFIGURATION_TYPES before using the project
command to make it work for Visual Studio.

Thanks,
Claus