gistfile1.txt

[01:01P][jwatzman@jwatzman-mba:/tmp] $ cat foo.cpp 
extern "C" void configure_link_extern_weak_test() __attribute__((weak));
int main(int argc, char** argv) {
	return configure_link_extern_weak_test == nullptr;
}
[01:01P][jwatzman@jwatzman-mba:/tmp] $ g++-4.8 foo.cpp
foo.cpp: In function 'int main(int, char**)':
foo.cpp:3:44: error: 'nullptr' was not declared in this scope
  return configure_link_extern_weak_test == nullptr;
                                            ^
[01:01P][jwatzman@jwatzman-mba:/tmp] $ g++-4.8 --std=gnu++0x foo.cpp 
Undefined symbols for architecture x86_64:
  "_configure_link_extern_weak_test", referenced from:
      _main in ccVm5bnn.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status