Fix the fsyntax-only required by rootcling

Ugly hack to avoid the default of ProgramAction which is SyntaxOnly
and we can't override it later. This will be fixed once cling is 
supports the latest changes in the clang's driver


git-svn-id: http://root.cern.ch/svn/root/trunk@42037 27541ba8-7e3a-0410-8455-c3a389f83636