Work around GCC bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58192

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

@@ -119,10 +119,10 @@ struct WirePointer {
   // -----------------------------------------------------------------
   // Part of pointer that depends on the kind.
 
-  union {
-    uint32_t upper32Bits;
-
-    struct {
+  // Note:  Originally StructRef, ListRef, and FarRef were unnamed types, but this somehow
+  //   tickled a bug in GCC:
+  //     http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58192
+  struct StructRef {
     WireValue<WordCount16> dataSize;
     WireValue<WirePointerCount16> ptrCount;
 
@@ -138,10 +138,9 @@ struct WirePointer {
       dataSize.set(size.data);
       ptrCount.set(size.pointers);
     }
-    } structRef;
-    // Also covers capabilities.
+  };
 
-    struct {
+  struct ListRef {
     WireValue<uint32_t> elementSizeAndCount;
 
     KJ_ALWAYS_INLINE(FieldSize elementSize() const) {
@@ -164,15 +163,25 @@ struct WirePointer {
       elementSizeAndCount.set(((wc / WORDS) << 3) |
                               static_cast<int>(FieldSize::INLINE_COMPOSITE));
     }
-    } listRef;
+  };
 
-    struct {
+  struct FarRef {
     WireValue<SegmentId> segmentId;
 
     KJ_ALWAYS_INLINE(void set(SegmentId si)) {
       segmentId.set(si);
     }
-    } farRef;
+  };
+
+  union {
+    uint32_t upper32Bits;
+
+    StructRef structRef;
+    // Also covers capabilities.
+
+    ListRef listRef;
+
+    FarRef farRef;
   };
 
   KJ_ALWAYS_INLINE(bool isNull() const) {