[INTERNAL] #1320: Give a nice error message for people who don't use the SeqanBuildSystem.cmake
[INTERNAL] #1320: Give a nice error message for people who don't use the SeqanBuildSystem.cmake

xenigmax/seqan,bestrauc/seqan,xenigmax/seqan,bestrauc/seqan,bestrauc/seqan,xenigmax/seqan,xenigmax/seqan,xenigmax/seqan,bestrauc/seqan,bestrauc/seqan,xenigmax/seqan,xenigmax/seqan,xenigmax/seqan,bestrauc/seqan,bestrauc/seqan,bestrauc/seqan