fix a really subtle bug in the cross section of aliases and TLS:

fix a really subtle bug in the cross section of aliases and TLS:
the SelectionDAG::getGlobalAddress function properly looks through
aliases to determine thread-localness, but then passes the GV* down
to GlobalAddressSDNode::GlobalAddressSDNode which does not.  Instead
of passing down isTarget, just pass down the predetermined node
opcode.  This fixes some assertions with out of tree changes I'm
working on.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74325 91177308-0d34-0410-b5e6-96231b3b80d8