[Bug c++/66445] New: [5/6 Regression] ICE with lambda in stmt expression in a template

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66445

            Bug ID: 66445
           Summary: [5/6 Regression] ICE with lambda in stmt expression in
                    a template
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
                CC: jason at gcc dot gnu.org
  Target Milestone: ---

template <typename> void foo ()
{
  auto a = ({ [=] {}; });
}

ICEs with -std=c++11 as well as -std=c++14 starting with r217748.
The diagnostics is:
rh1228916.ii: In function âvoid fn1()â:
rh1228916.ii:3:24: sorry, unimplemented: unexpected AST of kind type_decl
   auto a = ({ [=] {}; });
                        ^
rh1228916.ii:3:24: internal compiler error: in potential_constant_expression_1,
at cp/constexpr.c:4235