thread-safe issue (gmp 6.0.0)

[tg at gmplib.org]

paul zimmermann <Paul.Zimmermann at inria.fr> writes:

  If I replace FFT_TABLE_ATTRS by simply "const", valgrind --tool=helgrind
  becomes happy.
  
This is clearly a buglet in GMP.

It is harmless since the value written to the local variable will always
be the same.

Looking at the code now, it is not at all clear why we mess around with
FFT_TABLE_ATTRS.  It is never overridden, so we might as well get rid of
it.

-- 
Torbjörn
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