gh-116874: Fix building _decimal module on ppc64le

[georgthegreat]

In file included from python3/Modules/_decimal/libmpdec/basearith.c:34:
In file included from python3/Modules/_decimal/libmpdec/basearith.h:34:
python3/Modules/_decimal/libmpdec/typearith.h:612:4: error: "adapt mul_size_t() and mulmod_size_t()"
  #error "adapt mul_size_t() and mulmod_size_t()"
   ^
2 errors generated.

• Issue: Fix building CPython on ppc64le #116874

[georgthegreat]

This is the list of possible macros.

I have experienced the problem with clang-16.

[zware]

Rather than messing with the bundled copy of libmpdec, I would highly recommend migrating to building with ./configure --with-system-libmpdec, which is intended to become the default soon (see #115119).

[georgthegreat]

We build python from source and using system library is a less favorable option for us.
Bundle libmpdec works just fine as CPython is the only binary needing it.

Anyway, the problem is in libmpdec upstream, yet I do not have the way to upstream the fix there.

[vstinner]

Such change should be done upstream first: https://www.bytereef.org/mpdecimal/

[georgthegreat]

Such change should be done upstream first: https://www.bytereef.org/mpdecimal/

How do I contribute to mpdecimal?
Do they even have an upstream?

[vstinner]

How do I contribute to mpdecimal?

I suggest starting at https://www.bytereef.org/mpdecimal/mailinglists.html

Or you can contact directly Stefan Krah.

Do they even have an upstream?

I don't think that there is a public code repository.