Work around apparent bug in Debian GCC 4.9.2.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=781060

c++/src/capnp/capability-test.c++

@@ -510,6 +510,14 @@ public:
             // Too lazy to write a whole separate test for each of these cases...  so just make
             // sure they both compile here, and only actually test the latter.
             box.set("cap", kj::heap<TestExtendsDynamicImpl>(callCount));
+#if __GNUG__ && !__clang__
+            // The last line in this block tickles a bug in Debian G++ 4.9.2:
+            //     https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=781060
+            // For the moment, we can get away with skipping it as the previous line will set
+            // things up in a way that allows the test to complete successfully.
+            // TODO(soon): Remove this #if block when the bug is fixed.
+            return;
+#endif
             box.set("cap", kj::heap<TestExtendsImpl>(callCount));
           });
     } else {