Include required async utility code wherever it's used, not just by accident.

Closes #2075.

Cython/Compiler/Nodes.py

@@ -4232,6 +4232,9 @@ class GeneratorBodyDefNode(DefNode):
         # on normal generator termination, we do not take the exception propagation
         # path: no traceback info is required and not creating it is much faster
         if not self.is_inlined and not self.body.is_terminator:
+            if self.is_async_gen_body:
+                code.globalstate.use_utility_code(
+                    UtilityCode.load_cached("StopAsyncIteration", "Coroutine.c"))
             code.putln('PyErr_SetNone(%s);' % (
                 '__Pyx_PyExc_StopAsyncIteration' if self.is_async_gen_body else 'PyExc_StopIteration'))
         # ----- Error cleanup
@@ -5918,6 +5921,8 @@ class ReturnStatNode(StatNode):
             if self.return_type.is_pyobject:
                 if self.in_generator:
                     if self.in_async_gen:
+                        code.globalstate.use_utility_code(
+                            UtilityCode.load_cached("StopAsyncIteration", "Coroutine.c"))
                         code.put("PyErr_SetNone(__Pyx_PyExc_StopAsyncIteration); ")
                     code.putln("%s = NULL;" % Naming.retval_cname)
                 else:

Cython/Utility/AsyncGen.c

@@ -102,6 +102,7 @@ static int __Pyx_async_gen_init_hooks(__pyx_PyAsyncGenObject *o) {
 //////////////////// AsyncGenerator ////////////////////
 //@requires: AsyncGeneratorInitFinalizer
 //@requires: Coroutine.c::Coroutine
+//@requires: Coroutine.c::ReturnWithStopIteration
 //@requires: ObjectHandling.c::PyObjectCallMethod1
 
 

tests/compile/min_async.pyx

+# Need to include all utility code !
+
+async def sleep(x):
+    pass
+
+
+async def call():
+    await sleep(1)
+    yield