[Bug libstdc++/97869] New: defines __cpp_lib_span even when doesn't provide an implementation

[rs2740 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97869

            Bug ID: 97869
           Summary: <version> defines __cpp_lib_span even when <span>
                    doesn't provide an implementation
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com
  Target Milestone: ---

<version> defines __cpp_lib_span if __cplusplus > 201703L and _GLIBCXX_HOSTED,
but <span> only provides a definition of std::span when __cpp_lib_concepts is
defined.