Add C++ namespace definitions.

Signed-off-by: Keith Rothman <[email protected]>

Author: litghost

interchange/LogicalNetlist.capnp

@@ -18,6 +18,9 @@ using Ref = import "References.capnp";
 $Java.package("com.xilinx.rapidwright.interchange");
 $Java.outerClassname("LogicalNetlist");
 
+using Cxx = import "/capnp/c++.capnp";
+$Cxx.namespace("LogicalNetlist");
+
 struct HashSet {
     type  @0 : Ref.ImplementationType = enumerator;
     hide  @1 : Bool = true;

interchange/PhysicalNetlist.capnp

@@ -11,13 +11,16 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
 @0xcb2ccd67aa912968;
 using Java = import "/capnp/java.capnp";
-using Ref = import "References.capnp";
 $Java.package("com.xilinx.rapidwright.interchange");
 $Java.outerClassname("PhysicalNetlist");
 
+using Cxx = import "/capnp/c++.capnp";
+$Cxx.namespace("PhysicalNetlist");
+
+using Ref = import "References.capnp";
+
 struct StringRef {
     type  @0 :Ref.ReferenceType = rootValue;
     field @1 :Text = "strList";