Add flags to enable IEEE1800-2017 and IEEE1800-2023 languages generations
and also support them in the `begin_keywords macro. Since neither defines
new keywords they'll use the same keyword mask as 2012.
Update the driver, compiler, documentation and regression test harness so
-g2017 and -g2023 are recognized as language generation flags.
There are no specific features from these versions added yet, this is just
the necessary infrastructure to allow gating new features from those
generations when they are added later.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
eadb1d24ae