Add these missing functions

I'm only seeing "undefined reference to ..." errors in the CMake
build on a specific machine; I'm not sure why they're only cropping
up in that scenario.

I think these functions are only referenced from dead functions,
and in other environments the chains get dead-stripped.

src/capi/object.cpp

@@ -63,4 +63,8 @@ extern "C" PyObject* PyObject_Str(PyObject* v) {
     assert(PyString_Check(res));
     return res;
 }
+
+extern "C" PyObject* PyObject_SelfIter(PyObject* obj) {
+    Py_FatalError("unimplemented");
+}
 }

src/runtime/file.cpp

@@ -199,6 +199,10 @@ extern "C" int _PyFile_SanitizeMode(char* mode) {
     Py_FatalError("unimplemented");
 }
 
+extern "C" int PyObject_AsFileDescriptor(PyObject* o) {
+    Py_FatalError("unimplemented");
+}
+
 void setupFile() {
     file_cls->giveAttr("__name__", boxStrConstant("file"));