[Bug libstdc++/94971] New: [10/11 Regression] Parallel Mode cannot be used in C++20

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94971

            Bug ID: 94971
           Summary: [10/11 Regression] Parallel Mode cannot be used in
                    C++20
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

This fails to compile in C++20 mode:

#define _GLIBCXX_PARALLEL 1
#include <algorithm>

The new std::lexicographical_compare_three_way algo I added is in the wrong
namespace.