[lmi] Removing empty messages from static_assert()

[Vadim Zeitlin]

 Hello,

 Now that we require C++17, and already use its "terse static_assert"
(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3928.pdf) feature
in some places, there is no reason not to use it everywhere.

 Would you mind if I submitted a trivial patch removing all of these ""
from static_assert? This wouldn't result in any real changes, but it's just
annoying to see these empty strings in many places. The only problem is
that such a patch would need to be applied relatively quickly, as it would
touch a lot of files and so the risk of it getting out of date would be
relatively high.

 Please let me know if you'd like to do this now or postpone it until a
better time, thanks,
VZ