Fix a nasty bug that Nate ran into. In particular, instead of emitting a 2+MB

error message, print out:

llvm-link: error linking in 'g.2.rbc': Global Variable Collision on
' %struct.D_Reduction* %d_reduction_10_gram' - External linkage globals have
different initializers

That's a bit more concise, huh?

llvm-svn: 15958