Ricardo Wurmus <rekado@elephly.net> writes:

> avr-toolchain-5.5.0 fails to build.  It seems to be mixing headers from
> GCC 5 and GCC 7:
>
> --8<---------------cut here---------------start------------->8---
> In file included from /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:36:0,
>                  from ../../gcc-5.5.0/libcpp/system.h:214,
>                  from ../../gcc-5.5.0/libcpp/directives.c:22:
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:118:11: error: ‘::div_t’ has not been declared
>    using ::div_t;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:119:11: error: ‘::ldiv_t’ has not been declared
>    using ::ldiv_t;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:121:11: error: ‘::abort’ has not been declared
>    using ::abort;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:122:11: error: ‘::abs’ has not been declared
>    using ::abs;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:123:11: error: ‘::atexit’ has not been declared
>    using ::atexit;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:129:11: error: ‘::atof’ has not been declared
>    using ::atof;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:130:11: error: ‘::atoi’ has not been declared
>    using ::atoi;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:131:11: error: ‘::atol’ has not been declared
>    using ::atol;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:132:11: error: ‘::bsearch’ has not been declared
>    using ::bsearch;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:133:11: error: ‘::calloc’ has not been declared
>    using ::calloc;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:134:11: error: ‘::div’ has not been declared
>    using ::div;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:135:11: error: ‘::exit’ has not been declared
>    using ::exit;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:136:11: error: ‘::free’ has not been declared
>    using ::free;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:137:11: error: ‘::getenv’ has not been declared
>    using ::getenv;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:138:11: error: ‘::labs’ has not been declared
>    using ::labs;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:139:11: error: ‘::ldiv’ has not been declared
>    using ::ldiv;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:140:11: error: ‘::malloc’ has not been declared
>    using ::malloc;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:142:11: error: ‘::mblen’ has not been declared
>    using ::mblen;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:143:11: error: ‘::mbstowcs’ has not been declared
>    using ::mbstowcs;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:144:11: error: ‘::mbtowc’ has not been declared
>    using ::mbtowc;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:146:11: error: ‘::qsort’ has not been declared
>    using ::qsort;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:152:11: error: ‘::rand’ has not been declared
>    using ::rand;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:153:11: error: ‘::realloc’ has not been declared
>    using ::realloc;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:154:11: error: ‘::srand’ has not been declared
>    using ::srand;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:155:11: error: ‘::strtod’ has not been declared
>    using ::strtod;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:156:11: error: ‘::strtol’ has not been declared
>    using ::strtol;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:157:11: error: ‘::strtoul’ has not been declared
>    using ::strtoul;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:158:11: error: ‘::system’ has not been declared
>    using ::system;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:160:11: error: ‘::wcstombs’ has not been declared
>    using ::wcstombs;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:161:11: error: ‘::wctomb’ has not been declared
>    using ::wctomb;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:168:10: error: ‘ldiv_t’ does not name a type
>    inline ldiv_t
>           ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:214:11: error: ‘::lldiv_t’ has not been declared
>    using ::lldiv_t;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:220:11: error: ‘::_Exit’ has not been declared
>    using ::_Exit;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:224:11: error: ‘::llabs’ has not been declared
>    using ::llabs;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:226:10: error: ‘lldiv_t’ does not name a type
>    inline lldiv_t
>           ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:230:11: error: ‘::lldiv’ has not been declared
>    using ::lldiv;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:241:11: error: ‘::atoll’ has not been declared
>    using ::atoll;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:242:11: error: ‘::strtoll’ has not been declared
>    using ::strtoll;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:243:11: error: ‘::strtoull’ has not been declared
>    using ::strtoull;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:245:11: error: ‘::strtof’ has not been declared
>    using ::strtof;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:246:11: error: ‘::strtold’ has not been declared
>    using ::strtold;
>            ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:254:22: error: ‘__gnu_cxx::lldiv_t’ has not been declared
>    using ::__gnu_cxx::lldiv_t;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:256:22: error: ‘__gnu_cxx::_Exit’ has not been declared
>    using ::__gnu_cxx::_Exit;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:258:22: error: ‘__gnu_cxx::llabs’ has not been declared
>    using ::__gnu_cxx::llabs;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:259:22: error: ‘__gnu_cxx::div’ has not been declared
>    using ::__gnu_cxx::div;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:260:22: error: ‘__gnu_cxx::lldiv’ has not been declared
>    using ::__gnu_cxx::lldiv;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:262:22: error: ‘__gnu_cxx::atoll’ has not been declared
>    using ::__gnu_cxx::atoll;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:263:22: error: ‘__gnu_cxx::strtof’ has not been declared
>    using ::__gnu_cxx::strtof;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:264:22: error: ‘__gnu_cxx::strtoll’ has not been declared
>    using ::__gnu_cxx::strtoll;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:265:22: error: ‘__gnu_cxx::strtoull’ has not been declared
>    using ::__gnu_cxx::strtoull;
>                       ^
> /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0/include/c++/cstdlib:266:22: error: ‘__gnu_cxx::strtold’ has not been declared
>    using ::__gnu_cxx::strtold;
>                       ^
> In file included from ../../gcc-5.5.0/libcpp/system.h:214:0,
>                  from ../../gcc-5.5.0/libcpp/directives.c:22:
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:38:12: error: ‘std::abort’ has not been declared
>  using std::abort;
>             ^
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:39:12: error: ‘std::atexit’ has not been declared
>  using std::atexit;
>             ^
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:40:12: error: ‘std::exit’ has not been declared
>  using std::exit;
>             ^
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:51:12: error: ‘std::div_t’ has not been declared
>  using std::div_t;
>             ^
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:52:12: error: ‘std::ldiv_t’ has not been declared
>  using std::ldiv_t;
>             ^
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:55:12: error: ‘std::atof’ has not been declared
>  using std::atof;
>             ^
> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/stdlib.h:56:12: error: ‘std::atoi’ has not been declared
>  using std::atoi;
> --8<---------------cut here---------------end--------------->8---

Fixed in fd96ae4a709c5509f2d78af3968d64fe805ad1ef, thanks!