Broad valgrind run

[Torbjörn Granlund]

Perhaps our private red-zones are obsolete now that we have valgrind and
also vaeious memcheck compiler features?

I am not familiar with the valgrind annotations you're using and what
benefits they might bring.  It would be nice to not require code
annotations, as these take time to write, debug and maintain.

An alternative to valgrind is gcc's -fsanitize=address and similar
options to clang (assuming we can find a clang usable for GMP
compilation).  Here too, we shoiuld probably remove our private
red-zones.

-- 
Torbjörn
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