[lmi] PATCH: use std::uncaught_exceptions()

[Vadim Zeitlin]

 Hello,

 I've made a PR with a trivial change replacing the use of
std::uncaught_exception() (singular, returning bool) with
std::uncaught_exceptions() (plural, returning int) as the former is
deprecated in C++17 in favour of the latter and, in practice, MSVS 2017
warns about this, which is annoying, so it would be nice if you could
please apply https://github.com/vadz/lmi/pull/76

 Thanks in advance,
VZ