Cleanup: correct usage of extern-C blocks in various places

This removes extern-C blocks around other includes and adds
such blocks for some headers that need them.

source/blender/python/intern/bpy_operator_wrap.h

@@ -23,6 +23,10 @@
 
 struct wmOperatorType;
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* these are used for operator methods, used by bpy_operator.c */
 PyObject *PYOP_wrap_macro_define(PyObject *self, PyObject *args);
 
@@ -30,4 +34,8 @@ PyObject *PYOP_wrap_macro_define(PyObject *self, PyObject *args);
 void BPY_RNA_operator_wrapper(struct wmOperatorType *ot, void *userdata);
 void BPY_RNA_operator_macro_wrapper(struct wmOperatorType *ot, void *userdata);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif