Change Details

``` This only seems to be a win on 64-bit platforms, so only do it there. ``` Partial backport of secp256k1#831: https://github.com/bitcoin-core/secp256k1/pull/831/commits/b306935ac12bb24fd931d735b4dfc07f707e7447 Depends on D9409.

``` This only seems to be a win on 64-bit platforms, so only do it there. ``` Partial backport of [[https://github.com/bitcoin-core/secp256k1/pull/831 | secp256k1#831]]: https://github.com/bitcoin-core/secp256k1/pull/831/commits/b306935ac12bb24fd931d735b4dfc07f707e7447 Depends on D9409.

``` This only seems to be a win on 64-bit platforms, so only do it there. ``` Partial backport of [[https://github.com/bitcoin-core/secp256k1/pull/831 | secp256k1#831:]]: https://github.com/bitcoin-core/secp256k1/pull/831/commits/b306935ac12bb24fd931d735b4dfc07f707e7447 Depends on D9409.