User drivers based on llvmc must all share the initialization code.
Putting main() into libCompilerDriver is not a very good idea IMO (and ld gave
me some strange EH-related error anyway).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65825 91177308-0d34-0410-b5e6-96231b3b80d8