[Bug c++/59123] New: [c++11] can't forward-declare an object later defined constexpr

[eric.niebler at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59123

            Bug ID: 59123
           Summary: [c++11] can't forward-declare an object later defined
                    constexpr
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric.niebler at gmail dot com

Clang accepts the following. I think it's legal. g++ 4.8.1 rejects it:

// Fwd-declarations
struct S;
extern const S s;

// (... later) definitions
struct S {};
constexpr S s {};