Building lz4 as root was causing `make clean` to fail with permission
errors.
We used to have to install lz4 from source back in Ubuntu 14.04, but
nowadays the installed lz4 is fine. Get rid of ancient helpers and
cruft!
There was no memory barrier between writing and reading `done`, which
would allow reordering to cause races. With so little data to handle
after each job completes, we might as well just join.
Previously, parallel_compression would only handle each job's results
after ALL jobs were successfully queued. This caused all src/dst
buffers to remain in memory until then!
It also polled to check whether a job completed, which is racy without
any memory barrier.
Now, we flush results as a side effect of completing a job. Completed
frames are placed in an ordered linked-list, and any eligible frames
are flushed. This may be zero or multiple frames, depending on the
order in which jobs finish.
This design also makes it simple to support streaming input, so that
is now available. Just pass `-` as the filename, and stdin/stdout will
be used for I/O.
Some of these examples are intended to be parallel, and don't make
sense to link against single-threaded libzstd.
The filename of mt and nomt libzstd are identical, so it's still
possible to link against the single-threaded one, just harder.
