[Bug c++/83919] New: [8 regression] spurious -Wignored-qualifiers warning

[sss@li-snyder.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83919

            Bug ID: 83919
           Summary: [8 regression] spurious -Wignored-qualifiers warning
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sss@li-snyder.org
  Target Milestone: ---

With gcc version 
gcc version 8.0.1 20180115 (experimental) (GCC) 

compiling this source with -Wextra -std=c++17 gets a warning:

-- x.cc -----------------------------------------
enum class Conf;
struct foo
{
  foo (const Conf& conf) : x{conf} {}
  const Conf x;
};
--------------------------------------------------

$ ~/gcc/build/gcc/cc1plus -quiet x.cc -Wextra  -std=c++17 
x.cc: In constructor ‘foo::foo(const Conf&)’:
x.cc:4:34: warning: type qualifiers ignored on cast result type
[-Wignored-qualifiers]
   foo (const Conf& conf) : x{conf} {}
                                  ^

I don't see any obvious reason why this should give a warning.

The warning goes away if one uses x(conf) rather than x{conf} in the
initialization.  I also do not see this warning with gcc 7.2.1.