Add thread.interrupt_main

Tk application need this method to stop main window and to some other
things.

Author: Boxiang Sun

src/runtime/builtin_modules/thread.cpp

@@ -198,6 +198,12 @@ Box* getIdent() {
     return boxInt(pthread_self());
 }
 
+Box* interruptMain() {
+    PyErr_SetInterrupt();
+    Py_INCREF(Py_None);
+    return Py_None;
+}
+
 Box* stackSize() {
     Py_FatalError("unimplemented");
 }
@@ -227,6 +233,9 @@ void setupThread() {
                                              FunctionMetadata::create((void*)getIdent, BOXED_INT, 0), "get_ident"));
     thread_module->giveAttr("stack_size", new BoxedBuiltinFunctionOrMethod(
                                               FunctionMetadata::create((void*)stackSize, BOXED_INT, 0), "stack_size"));
+    thread_module->giveAttr("interrupt_main", new BoxedBuiltinFunctionOrMethod(
+                FunctionMetadata::create((void*)interruptMain, UNKNOWN, 0), "interrupt_main"
+                ));
     thread_module->giveAttr("_count", new BoxedBuiltinFunctionOrMethod(
                                           FunctionMetadata::create((void*)threadCount, BOXED_INT, 0), "_count"));