[Bug libstdc++/70483] New: string_view::compare and coparision operators are not constexpr

["sir.vestnik at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70483

            Bug ID: 70483
           Summary: string_view::compare and coparision operators are not
                    constexpr
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sir.vestnik at gmail dot com
  Target Milestone: ---

libstdc++ std::experimental::basic_string_view implementation mising a lot of
constexpr specifications (according to the n4480) for example commented out
static assert here
https://github.com/VestniK/cpp-metainf/blob/master/pretty_func_parse/member_name.h
is valid and can be compiled with clang libc++ but fails to compile with gcc
libstdc++