Avoid unused C variable warning by moving declaration and usage under the same condition.

Closes https://github.com/cython/cython/pull/3763

Cython/Compiler/ModuleNode.py

@@ -1866,13 +1866,13 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         code.putln(
             "static int %s(PyObject *o, PyObject *i, PyObject *v) {" % (
                 scope.mangle_internal("mp_ass_subscript")))
-        code.putln(
-            "__Pyx_TypeName o_type_name;")
         code.putln(
             "if (v) {")
         if set_entry:
             code.putln("return %s(o, i, v);" % set_entry.func_cname)
         else:
+            code.putln(
+                "__Pyx_TypeName o_type_name;")
             self.generate_guarded_basetype_call(
                 base_type, "tp_as_mapping", "mp_ass_subscript", "o, i, v", code)
             code.putln(
@@ -1894,6 +1894,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 "return %s(o, i);" % (
                     del_entry.func_cname))
         else:
+            code.putln(
+                "__Pyx_TypeName o_type_name;")
             self.generate_guarded_basetype_call(
                 base_type, "tp_as_mapping", "mp_ass_subscript", "o, i, v", code)
             code.putln(
@@ -1941,8 +1943,6 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         code.putln(
             "static int %s(PyObject *o, Py_ssize_t i, Py_ssize_t j, PyObject *v) {" % (
                 scope.mangle_internal("sq_ass_slice")))
-        code.putln(
-            "__Pyx_TypeName o_type_name;")
         code.putln(
             "if (v) {")
         if set_entry:
@@ -1950,6 +1950,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 "return %s(o, i, j, v);" % (
                     set_entry.func_cname))
         else:
+            code.putln(
+                "__Pyx_TypeName o_type_name;")
             self.generate_guarded_basetype_call(
                 base_type, "tp_as_sequence", "sq_ass_slice", "o, i, j, v", code)
             code.putln(
@@ -1971,6 +1973,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 "return %s(o, i, j);" % (
                     del_entry.func_cname))
         else:
+            code.putln(
+                "__Pyx_TypeName o_type_name;")
             self.generate_guarded_basetype_call(
                 base_type, "tp_as_sequence", "sq_ass_slice", "o, i, j, v", code)
             code.putln(