ClangImporter: repair build on Windows

Explicitly apply the std::move as the signature of the callee is:
  void swift::Evaluator::cacheOutput<swift::ExtendedNominalRequest, _>(const Request &, swift::NominalTypeDecl *&&)

The second formal parameter here is a `swift::ClassDecl` which is a
subclass of NominalTypeDecl, however, the cast will construct a
`swift::NominalTypeDecl *`.  This is a lvalue and cannot be bound to a
r-value reference.  Explicitly construct the r-value reference via
`std::move`.

Author: compnerd

lib/ClangImporter/ImportDecl.cpp

@@ -4550,7 +4550,7 @@ namespace {
       Impl.SwiftContext.evaluator.cacheOutput(ExtendedTypeRequest{result},
                                               objcClass->getDeclaredType());
       Impl.SwiftContext.evaluator.cacheOutput(ExtendedNominalRequest{result},
-                                              objcClass);
+                                              std::move(objcClass));
 
       // Determine the type and generic args of the extension.
       if (objcClass->getGenericParams()) {