Add new variable SYSTEM_INCLUDE_DIRECTORIES. Put include directories not belonging to our project from BASE_INCLUDE_DIRECTORIES in SYSTEM_INCLUDE_DIRECTORIES.
Get rid of warnings which come from include files which doesn't belong to FairRoot. These are for example Boost or ROOT includes. Define in all CMakeLists.txt files such libraries as system libraries. In this case the compiler will not produce any warning. This change reduces the nightly test time on some machines from more then hour to 1 minute. The reason for this long compile time was the enormous amount of warnings produced before. The output of the warnings sum up to roughly 850 MB.