Fix r162835 as per Richard's comments.

VisitVarDecl should return Error(E), and we should test that the address
of a TLS var can't be used as a constexpr.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162837 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed