iostreams/test/code_converter_test does not compile with Xcode 6

[nat@…]

Apparently the bundled std::codecvt template has changed in a way incompatible with code_converter_test.

./b2 toolset=darwin variant=release address-model=32 -a -q architecture=x86 -sNO_BZIP2=1 libs/iostreams/test//code_converter_test
...
darwin.compile.c++ bin.v2/libs/iostreams/test/code_converter_test.test/darwin-4.2.1/release/address-model-32/architecture-x86/code_converter_test.o
In file included from libs/iostreams/test/code_converter_test.cpp:17:
In file included from ./boost/iostreams/code_converter.hpp:35:
./boost/iostreams/detail/codecvt_helper.hpp:217:25: error: implicit instantiation of undefined template 'std::__1::codecvt<wchar_t, char, boost::iostreams::tes\
t::null_padded_codecvt_state>'
struct codecvt_helper : std::codecvt<Intern, Extern, State> {
                        ^

This same error occurs with debug and 64-bit builds.

This is not a regression: the same failure occurs with Boost 1.55.0.

[anonymous]

The issue is reproducible with Boost 1.55.0 on Mac OS X 10.9.5, Xcode 5.1: In file included from code_converter_test.cpp(39): ../../../boost/iostreams/detail/codecvt_helper.hpp(217): error: incomplete type is not allowed

struct codecvt_helper : std::codecvt<Intern, Extern, State> {

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