Next step: Only pad debug_line when the target is darwin. Add a FIXME to avoid

Next step: Only pad debug_line when the target is darwin. Add a FIXME to avoid
doing that if the target is darwin10 or newer.

This fixes
*) Direct object emission was producing objects without the workaround on
   darwin9.
*) Assembly printing was producing objects with the workaround on linux.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120866 91177308-0d34-0410-b5e6-96231b3b80d8