gcc5 libstdc++ abi transition breaks clang building against libstdc++, the default in debian

[Stefan Bühler <source@stbuehler.de>]

Hi,

clang doesn't support the abi_tag attribute, see:
https://llvm.org/bugs/show_bug.cgi?id=23529

And yet I couldn't find a single bug report in debians llvm packages
mentioning this problem; I think it was irresponsible to push the
transition while such bugs are not fixed.

Compiling with clang is an important way to keep code quality up (as it
has more or at least other static code analysis features), and so this
is a loss whether clang is used to build the final binary or not.

(My current use case is building against boost unit_test_framework:
std::string boost::unit_test::ut_detail::normalize_test_case_name(boost::unit_test::basic_cstring<char const>)
is tagged [abi:cxx11] by gcc in the debian package, and clang doesn't find it)

regards,
Stefan