build_id: cache the value
build_id: cache the value

The CPU cost of iterating over the relevant ELF structures is probably
negligible (despite the amount of code involved), but there is no need
to keep the containing page mapped in RAM when it doesn't have to be.

Signed-off-by: Michael Livshin <ae60993c65de9cdf2ca07b7426c976808535d555@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla