Merge pull request #8730 from tcclevenger/custom-mg-constraints

add interface for user defined GMG constraints

diff --cc source/lac/affine_constraints.inst.in
index 27006ee16442303edf6889a321f2db2605b6f78d,e3877ee611d95fe0f4e23180eb1d74584e47e555..c5635d230bde436fe0990452efb07136899e1454
--- 1/source/lac/affine_constraints.inst.in
--- 2/source/lac/affine_constraints.inst.in
+++ b/source/lac/affine_constraints.inst.in
@@@ -329,17 -344,8 +329,21 @@@ for (T : DEAL_II_VEC_TEMPLATES
        T<float> &) const;
      template void dealii::AffineConstraints<double>::distribute<T<float>>(
        T<float> &) const;
+ 
+     template void dealii::AffineConstraints<double>::distribute<
+       LinearAlgebra::distributed::T<float>>(
+       LinearAlgebra::distributed::T<float> &) const;
    }
 +
 +
 +for (T : VECTOR_TYPES)
 +  {
 +    namespace internal
 +    {
 +      namespace AffineConstraintsImplementation
 +      {
 +        template void
 +        set_zero_all(const std::vector<types::global_dof_index> &, T &vec);
 +      \}
 +    \}
 +  }