global locale from boost make std::regex fail on FreeBSD with libc++

[schorsch1976]

This is a dependent of
#35
but with more concentrated and more distilled information.

bug.txt
result-csv.ods.tar.gz

The regex fails if one of this facets is set:
"all_characters , collation_facet, all_categories".

boost::locale::generator gen;

// all_characters , collation_facet, all_categories trigger the bug",
gen.categories(collation_facet);
std::locale loc{ gen("de_DE.UTF-8") };
std::locale::global(loc);

std::regex re_datetime("^Date\\s*:[\\s\\t]*(\\d{4}\\-\\d{2}\\-\\d{2} "
						"\\d{2}:\\d{2}:\\d{2}?)$",
						std::regex_constants::icase);
std::smatch match;
if (std::regex_match(test, match, re_datetime) && match.size() > 1)
	std::cout << "All ok" << std::endl;
else
	std::cout << "Bug triggered" << std::endl;

I setup a testprogram that tries every locale (192),every facet(12(no wchar_t on freebsd)), every backend(std/icu/posix) and icase on/off.

The pivot analysis of the result shows, this happens on every locale (except posix/C) with facet "all_characters , collation_facet, all_categories".

This happens only on FreeBSD with clang and libc++.

[Flamefire]

Closing in favor of newer issue #249