[Bug c++/57640] New: Explicit call of system literal operator complains about leading underscore.

[3dw4rd at verizon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57640

            Bug ID: 57640
           Summary: Explicit call of system literal operator complains
                    about leading underscore.
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 3dw4rd at verizon dot net

Since we added literal operators to the standard library I noticed that
if you explicitly call a std literal operator
-----------------------------------------------------------
#include <chrono>

using namespace std::literals::chrono_literals;

auto blooper = operator"" min(45.0L);
-----------------------------------------------------------
you get
-----------------------------------------------------------
blooper.cc:5:27: warning: literal operator suffixes not preceded by ‘_’ are
reserved for future standardization [enabled by default]
 auto blooper = operator"" min(45.0L);
-----------------------------------------------------------

The definition in the system header doesn't trigger this but the explicit call
in user code does.

Mot fatal, and won't be commonly hit butI'd like to fix it.