The uncached lookup is mainly used in the ASTImporter/LLDB code-path
where we're not allowed to load from external storage. When importing
a FieldDecl with a DeclContext that had no external visible storage
(but came from a Clang module or PCH) the above call to `lookup(Name)`
the regular `DeclContext::lookup` fails because:
1. `DeclContext::buildLookup` doesn't set `LookupPtr` for decls
that came from a module
2. LLDB doesn't use the `SharedImporterState`
In such a case we would never continue with the "slow" path of iterating
through the decl chain on the DeclContext. In some cases this means that
ASTNodeImporter::VisitFieldDecl ends up importing a decl into the
DeclContext a second time.
The patch removes the short-circuit in the case where we don't find
any decls via the regular lookup.
**Tests**
* Un-skip the failing LLDB API tests
Differential Revision: https://reviews.llvm.org/D133945
e456d2ba8b