Default to only building LLVM optimisations if the version of LLVM is tested.



git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/libobjc2/trunk@36225 72102866-910b-0410-8b05-ffd578937521
Fix optimisations with LLVM trunk.



git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/libobjc2/trunk@36226 72102866-910b-0410-8b05-ffd578937521