lld is multi-threaded in some phases, based on observation, it could
spawn up to 16 threads for each link job. and each job could take up
to more than 3 GiB memory in total. without the change, we can run
into OOM with a machine without abundant memory, so increase the
per-link-job mem accordingly.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
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