Bring the doc string C constant back for special methods, except for the buffer methods.

Cython/Compiler/Nodes.py

@@ -3443,7 +3443,7 @@ class DefNodeWrapper(FuncDefNode):
             if docstr.is_unicode:
                 docstr = docstr.as_utf8_string()
 
-            if with_pymethdef:
+            if with_pymethdef or (entry.is_special and entry.name not in ('__getbuffer__', '__releasebuffer__')):
                 code.putln('static char %s[] = %s;' % (
                     entry.doc_cname,
                     docstr.as_c_string_literal()))