[PATCH 4/3] improve detection of attribute conflicts (PR 81544)

[Martin Sebor]

Jon,

Attached is the libstdc++ only patch to remove the pointless
const attribute from __pool<true>::_M_destroy_thread_key(void*).

  https://gcc.gnu.org/ml/gcc/2017-08/msg00027.html

I only belatedly now broke it out of the larger patch under
review here:

  https://gcc.gnu.org/ml/gcc-patches/2017-08/msg00599.html

Thanks
Martin

libstdc++-v3/ChangeLog:

	PR c/81544
	* include/ext/mt_allocator.h (_M_destroy_thread_key): Remove
	pointless attribute const.

diff --git a/libstdc++-v3/include/ext/mt_allocator.h b/libstdc++-v3/include/ext/mt_allocator.h
index effb13b..f349ff8 100644
--- a/libstdc++-v3/include/ext/mt_allocator.h
+++ b/libstdc++-v3/include/ext/mt_allocator.h
@@ -355,7 +355,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
       // XXX GLIBCXX_ABI Deprecated
-      _GLIBCXX_CONST void 
+      void
       _M_destroy_thread_key(void*) throw ();
 
       size_t