More GCC fixes.

c++/src/capnp/capability.c++

@@ -30,7 +30,6 @@
 #include <kj/refcount.h>
 #include <kj/debug.h>
 #include <kj/vector.h>
-#include <kj/one-of.h>
 #include <map>
 
 namespace capnp {

c++/src/capnp/layout.c++

@@ -1712,7 +1712,7 @@ struct WireHelpers {
           goto useDefault;
         }
 
-        setCapabilityPointer(dstSegment, dst,
+        return setCapabilityPointer(dstSegment, dst,
             srcSegment->getArena()->extractCap(StructReader(
                 srcSegment, ptr,
                 reinterpret_cast<const WirePointer*>(ptr + src->structRef.dataSize.get()),
@@ -1727,6 +1727,8 @@ struct WireHelpers {
           goto useDefault;
         }
     }
+
+    KJ_UNREACHABLE;
   }
 
   static void adopt(SegmentBuilder* segment, WirePointer* ref, OrphanBuilder&& value) {

c++/src/kj/one-of.h

@@ -115,13 +115,13 @@ private:
   inline bool copyVariantFrom(const OneOf& other) {
     if (other.is<T>()) {
       ctor(*reinterpret_cast<T*>(space), other.get<T>());
-      tag = typeIndex<T>();
     }
     return false;
   }
   void copyFrom(const OneOf& other) {
     // Initialize as a copy of `other`.  Expects that `this` starts out uninitialized, so the tag
     // is invalid.
+    tag = other.tag;
     doAll(copyVariantFrom<Variants>(other)...);
   }
 
@@ -129,13 +129,13 @@ private:
   inline bool moveVariantFrom(OneOf& other) {
     if (other.is<T>()) {
       ctor(*reinterpret_cast<T*>(space), kj::mv(other.get<T>()));
-      tag = typeIndex<T>();
     }
     return false;
   }
   void moveFrom(OneOf& other) {
     // Initialize as a copy of `other`.  Expects that `this` starts out uninitialized, so the tag
     // is invalid.
+    tag = other.tag;
     doAll(moveVariantFrom<Variants>(other)...);
   }
 };