[patch] Add const to constexpr member function in regex.h

[Jonathan Wakely]

In C++14 constexpr member functions are no longer implicitly const.

Tested x86_64-linux, committed to trunk and 4.9

commit 63d852cc56aa0f44ee0f770594c79705331933ec
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Oct 8 09:34:15 2014 +0100

    	* include/bits/regex.h (regex_token_iterator::_M_end_of_seq): Add
    	const qualifier.

diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
index 4ec20d7..4244f2e 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -2689,7 +2689,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
       constexpr bool
-      _M_end_of_seq()
+      _M_end_of_seq() const
       { return _M_result == nullptr; }
 
       _Position         _M_position;