libhydrogen on Sonata only works in 32 bit mode

[PhilDay-CT]

Something in the 64-bit compile on Sonata means that it doesn't generate a valid signature, and always validates even invalid signatures.

Work around is to force it to compile in 32 bit mode, but based on a commend from David Chisnell it seems that 64-bit maths is exoecte to work on Sonata.

Maybe th emulti3() method we had to add to cheriot-rtos is wrong, and should have been implemented for int128_t (long long) rather than int64_t

[PhilDay-CT]

Signal discussion with David Chisnall suggested he thought that "long long" should be treated as int64_t on cheriot, and so the implementation of __multi3() is OK.

Raised an issue in cheriot LLVM for the compiler folks to consider: CHERIoT-Platform/llvm-project#52

[PhilDay-CT]

Identified as an issue in LLVM v13 that incorrectly defines SIZEOF_INT128_ in cheriot. Fixed in LLVM v17, which cheriot is moving to

[PhilDay-CT]

Tested a pre-release of the LLVM v17 environment and checked that it does correctly compile libhydrogen in 32-bit mode