TargetInfo::getSizeOfUnwindException wrong for CHERI

[jrtc27]

Our structure is twice as big (note that 32-bit still uses uint64_t so is the same as 64-bit) for L64PC128 and so this needs to be 64 not 32. The consequence of this is that catching a pointer to a non-record type by reference loads the pointer from the wrong place within the exception object: https://cheri-compiler-explorer.cl.cam.ac.uk/z/M5so3o crashes, but patching the 32 immediate to 64 works.