Blind fix for error with old Clang

<https://ci.libreoffice.org//job/lo_ubsan/1050/consoleFull#-18477798892a810015-1db5-427c-9ce2-83b5f06a5284>:

> In file included from /home/tdf/lode/jenkins/workspace/lo_ubsan/codemaker/source/codemaker/exceptiontree.cxx:28:
> /home/tdf/lode/jenkins/workspace/lo_ubsan/include/unoidl/unoidl.hxx:507:9: error: constructor for 'unoidl::SingleInterfaceBasedServiceEntity::Constructor' must explicitly initialize the const member 'annotations'
>         Constructor(): defaultConstructor(true) {}
>         ^
> /home/tdf/lode/jenkins/workspace/lo_ubsan/include/unoidl/unoidl.hxx:524:44: note: 'annotations' declared here
>         std::vector< rtl::OUString > const annotations;
                                           ^
1 error generated.

Change-Id: I041a67599b48959bcca136bab646f6943d071bed

include/unoidl/unoidl.hxx

@@ -15,6 +15,7 @@
 #include <cassert>
 #include <vector>
 
+#include <config_clang.h>
 #include <osl/mutex.hxx>
 #include <rtl/ref.hxx>
 #include <rtl/ustring.hxx>
@@ -504,7 +505,11 @@ public:
             bool const rest;
         };
 
-        Constructor(): defaultConstructor(true) {}
+        Constructor(): defaultConstructor(true)
+#if defined __clang__ && CLANG_VERSION == 30800
+                       , annotations()
+#endif
+        {}
 
         Constructor(
             rtl::OUString const & theName,