[python] Silence false positive self assigment warning

Possible bug in clang is tracked here:
https://bugs.llvm.org/show_bug.cgi?id=43124

dune/python/istl/bvector.hh

@@ -159,8 +159,20 @@ namespace Dune
       cls.def( "__len__", [] ( const BlockVector &self ) { return self.N(); } );
 
       cls.def( pybind11::self += pybind11::self );
+
+// silence a warning (false positive) emitted by clang
+// https://bugs.llvm.org/show_bug.cgi?id=43124
+#ifdef __clang__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wself-assign-overloaded"
+#endif
+
       cls.def( pybind11::self -= pybind11::self );
 
+#ifdef __clang__
+#pragma GCC diagnostic pop
+#endif
+
       detail::registerOneTensorInterface( cls );
       detail::registerISTLIterators( cls );