Attempting to recompute it are doomed to fail because the IDNS of a declaration
is not necessarily preserved across serialization and deserialization (in turn
because whether a friend declaration is visible depends on whether some prior
non-friend declaration exists).
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@321921 91177308-0d34-0410-b5e6-96231b3b80d8
Richard Smith