Make __PYX_WARN_IF_INIT_CALLED name unique per-module in generated header files (GH-4309)

Fixes https://github.com/cython/cython/issues/4308

Cython/Compiler/ModuleNode.py

@@ -311,12 +311,12 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             h_code_main.putln('__declspec(deprecated(%s)) __inline' % (
                 warning_string.as_c_string_literal()))
             h_code_main.putln('#endif')
-            h_code_main.putln("static PyObject* __PYX_WARN_IF_INIT_CALLED(PyObject* res) {")
+            h_code_main.putln("static PyObject* __PYX_WARN_IF_%s_INIT_CALLED(PyObject* res) {" % py3_mod_func_name)
             h_code_main.putln("return res;")
             h_code_main.putln("}")
             # Function call is converted to warning macro; uncalled (pointer) is not
-            h_code_main.putln('#define %s() __PYX_WARN_IF_INIT_CALLED(%s())' % (
-                py3_mod_func_name, py3_mod_func_name))
+            h_code_main.putln('#define %s() __PYX_WARN_IF_%s_INIT_CALLED(%s())' % (
+                py3_mod_func_name, py3_mod_func_name, py3_mod_func_name))
             h_code_main.putln('#endif')
             h_code_main.putln('#endif')
 

tests/run/include_multiple_modules.srctree

+PYTHON setup.py build_ext --inplace
+
+############# setup.py #############
+
+from Cython.Build.Dependencies import cythonize
+from distutils.core import setup
+
+setup(
+    ext_modules = cythonize(["a.pyx", "b.pyx", "include_both.pyx"]),
+    )
+
+############# a.pyx ###############
+
+cdef public f():
+    pass
+    
+############# b.pyx ###############
+
+cdef public g():
+    pass
+    
+############# include_both.pyx ####
+
+# This is just checking that a and b don't duplicate any names
+# and thus it's possible to include them both in one place
+
+cdef extern from "a.h":
+    pass
+    
+cdef extern from "b.h":
+    pass