Fix pr17056.

This makes llvm-nm ignore members that are not sufficiently aligned for
lib/Object to handle.

These archives are invalid. GNU AR is able to handle this, but in general
just warns about broken archive members.

We should probably start warning too, but for now just make sure llvm-nm
exits with an 0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211036 91177308-0d34-0410-b5e6-96231b3b80d8