[Bug libstdc++/79700] New: std::fabsf and std::fabsl missing from <cmath>

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79700

            Bug ID: 79700
           Summary: std::fabsf and std::fabsl missing from <cmath>
           Product: gcc
           Version: 6.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

#include <cmath>

using std::fabsf;
using std::fabsl;

abs.cc:3:12: error: ‘std::fabsf’ has not been declared
 using std::fabsf;
            ^~~~~
abs.cc:4:12: error: ‘std::fabsl’ has not been declared
 using std::fabsl;
            ^~~~~

These are required by C++17 (and maybe implicitly by C++11, although it's not
very clear)