ah, c++, even the simplest, most basic code I can imagine and...

gistfile1.txt

Undefined symbols for architecture x86_64:
  "std::__1::locale::use_facet(std::__1::locale::id&) const", referenced from:
      std::__1::ctype<char> const& std::__1::use_facet<std::__1::ctype<char> >(std::__1::locale const&) in main.o
      std::__1::ctype<char> const& std::__1::use_facet<std::__1::ctype<char> >(std::__1::locale const&) in decrypt_process.o
  "std::__1::ios_base::getloc() const", referenced from:
      std::__1::basic_ios<char, std::__1::char_traits<char> >::widen(char) const in main.o
      std::__1::basic_ios<char, std::__1::char_traits<char> >::widen(char) const in decrypt_process.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__init(unsigned long, char)", referenced from:
      std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string(unsigned long, char) in main.o
      std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string(unsigned long, char) in decrypt_process.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::~basic_string()", referenced from:
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) in main.o
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) in decrypt_process.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::put(char)", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::endl<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&) in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::endl<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&) in decrypt_process.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::flush()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::endl<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&) in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::endl<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&) in decrypt_process.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::sentry(std::__1::basic_ostream<char, std::__1::char_traits<char> >&)", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in decrypt_process.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::~sentry()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in decrypt_process.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::operator<<(void const*)", referenced from:
      std::__1::enable_if<is_same<void, std::__1::__void_t<decltype((declval<std::__1::basic_ostream<char, std::__1::char_traits<char> >&>()) << (declval<std::__1::unique_ptr<Thing, std::__1::default_delete<Thing> >::pointer>()))>::type>::value, std::__1::basic_ostream<char, std::__1::char_traits<char> >&>::type std::__1::operator<<<char, std::__1::char_traits<char>, Thing, std::__1::default_delete<Thing> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, std::__1::unique_ptr<Thing, std::__1::default_delete<Thing> > const&) in main.o
      std::__1::enable_if<is_same<void, std::__1::__void_t<decltype((declval<std::__1::basic_ostream<char, std::__1::char_traits<char> >&>()) << (declval<std::__1::unique_ptr<Gizmo, std::__1::default_delete<Gizmo> >::pointer>()))>::type>::value, std::__1::basic_ostream<char, std::__1::char_traits<char> >&>::type std::__1::operator<<<char, std::__1::char_traits<char>, Gizmo, std::__1::default_delete<Gizmo> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, std::__1::unique_ptr<Gizmo, std::__1::default_delete<Gizmo> > const&) in main.o
  "std::__1::cout", referenced from:
      _main in main.o
      Gizmo::~Gizmo() in main.o
      Gizmo::~Gizmo() in decrypt_process.o
  "std::__1::ctype<char>::id", referenced from:
      std::__1::ctype<char> const& std::__1::use_facet<std::__1::ctype<char> >(std::__1::locale const&) in main.o
      std::__1::ctype<char> const& std::__1::use_facet<std::__1::ctype<char> >(std::__1::locale const&) in decrypt_process.o
  "std::__1::locale::~locale()", referenced from:
      std::__1::basic_ios<char, std::__1::char_traits<char> >::widen(char) const in main.o
      std::__1::basic_ios<char, std::__1::char_traits<char> >::widen(char) const in decrypt_process.o
  "std::__1::ios_base::__set_badbit_and_consider_rethrow()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in decrypt_process.o
  "std::__1::ios_base::clear(unsigned int)", referenced from:
      std::__1::ios_base::setstate(unsigned int) in main.o
      std::__1::ios_base::setstate(unsigned int) in decrypt_process.o
  "std::terminate()", referenced from:
      ___clang_call_terminate in main.o
      ___clang_call_terminate in decrypt_process.o
  "operator delete(void*)", referenced from:
      std::__1::default_delete<Gizmo>::operator()(Gizmo*) const in main.o
      std::__1::default_delete<Thing>::operator()(Thing*) const in main.o
  "operator new(unsigned long)", referenced from:
      std::__1::__unique_if<Thing>::__unique_single std::__1::make_unique<Thing>() in main.o
      std::__1::__unique_if<Gizmo>::__unique_single std::__1::make_unique<Gizmo>() in main.o
  "___cxa_begin_catch", referenced from:
      ___clang_call_terminate in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.o
      ___clang_call_terminate in decrypt_process.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in decrypt_process.o
  "___cxa_end_catch", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in decrypt_process.o
  "___gxx_personality_v0", referenced from:
      _main in main.o
      std::__1::unique_ptr<Gizmo, std::__1::default_delete<Gizmo> >::unique_ptr<true, void>(Gizmo*) in main.o
      Gizmo::~Gizmo() in main.o
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.o
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) in main.o
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >::ostreambuf_iterator(std::__1::basic_ostream<char, std::__1::char_traits<char> >&) in main.o
      std::__1::basic_ios<char, std::__1::char_traits<char> >::widen(char) const in main.o
      ...
ld: symbol(s) not found for architecture x86_64