Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
std::gmtime() has a sad property of using a global static buffer
for returning its value. This is not thread-safe, so its usage
is replaced with gmtime_r, which can accept a local buffer.
While no regressions where observed in this particular area of code,
a similar bug caused failures in alternator, so it's better to simply
replace all std::gmtime calls with their thread-safe counterpart.
Message-Id: <39e91c74de95f8313e6bb0b12114bf12c0e79519.1588589151.git.sarna@scylladb.com>
This change fixes the dependencies between the clock implementation headers. All
the clocks share the common clock offset, but are otherwise independent (though
the `db_clock` does depend on `gc_clock` for time point conversions).
