Use shouldAssumeDSOLocal in classifyGlobalReference.

Use shouldAssumeDSOLocal in classifyGlobalReference.

And teach shouldAssumeDSOLocal that ppc has no copy relocations.

The resulting code handle a few more case than before. For example, it
knows that a weak symbol can be resolved to another .o file, but it
will still be in the main executable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293180 91177308-0d34-0410-b5e6-96231b3b80d8