XRay (-fxray-instrument) defaulted ON, adding ~45MB of sled sections to every
binary plus per-function sleds, and its composed R_AARCH64_PREL64 relocations
made llvm-bolt fail on aarch64 ("expected relocatable expression"). Disabling
it for the optimized build: binary 945MB->648MB after BOLT, RSS ~50MB vs the
official PGO+LTO+BOLT ClickHouse's ~116MB, faster on filters/aggregations, and
BOLT now runs clean on aarch64 (needs ulimit -s 2097152 for veneers).