[Bug c++/85689] New: if constexpr compiles false branch

[msharov at users dot sourceforge.net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85689

            Bug ID: 85689
           Summary: if constexpr compiles false branch
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msharov at users dot sourceforge.net
  Target Milestone: ---

int main (void)
{
    if constexpr (false)
        static_assert (false, "this should not be compiled");
    return 0;
}

g++ 8.1 fails compiling the branch with the static_assert even though if
constexpr condition is false. May be the same as #85149, but still present in
g++ 8.1.0 on Arch.