benchmarks/imb: not for 32 bit architectures
The code bases uses %lu or PRIu64 to print size_t values in various
places. Elsewhere it assumes size_t is 64 bits, such as when
evaluating ((size_t)1) << IMB_P2P_MAX_MSG_LOG where
IMB_P2P_MAX_MSG_LOG is greater than 31.
Approved by: portmgr (build fix blanket)
MFH: 2026Q2