[Bug libstdc++/67114] [MinGW64] build failure with POSIX threads enabled

[sliwa at ifpan dot edu.pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67114

--- Comment #3 from Cezary Śliwa <sliwa at ifpan dot edu.pl> ---
Yes, I understand. The purpose of the patch is to point the problem. In
particular I don't know why operator< is needed and what are the required
semantics (i.e. comparing pointers vs. comparing thread sequence numbers; what
is the x field in the struct?). I am also concerned if the current
implementation of pthread_equal in the w32-pthreads library is correct in this
respect.