SVN revision 186977 seem to have caused:

In file included from /build/regtest/gcc-head-build/s390-ibm-linux-gnu/libstdc++-v3/include/bits/stl_algo.h:68:0,
                 from /build/regtest/gcc-head-build/s390-ibm-linux-gnu/libstdc++-v3/include/algorithm:63,
                 from /build/regtest/gcc-head-build/s390-ibm-linux-gnu/libstdc++-v3/include/regex:38,
                 from /build/regtest/gcc-head/libstdc++-v3/src/c++11/regex.cc:25:
/build/regtest/gcc-head-build/s390-ibm-linux-gnu/libstdc++-v3/include/functional: In member function ‘std::__regex::_StateIdT std::__regex::_Nfa::_M_insert_accept()’:
/build/regtest/gcc-head-build/s390-ibm-linux-gnu/libstdc++-v3/include/functional:2057:63: internal compiler error: tree check: expected tree_vec, have error_mark in comp_template_args_with_info, at cp/pt.c:7038
  using _Requires = typename enable_if<_Cond::value, _Tp>::type;
                                                               ^
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See <http://gcc.gnu.org/bugs.html> for instructions.