Build GNUstep development environment ( including llvm/clang )
First build stable LLVM/Clang 3.3, by running llvm-build.sh.
It takes some time to download & compile.
Then build GNUstep environment, with libobjc2 and libdispatch supported,
by running gs-build.sh. It takes some time to download.
Finally you can test with the block-test.sh script.
If it is not crashing, then our build is working.