Remove use of deprecated register keyword, see: https://svn.boost.org/trac/boost/ticket/9640

include/boost/regex/v4/regex_raw_buffer.hpp

@@ -129,7 +129,7 @@ public:
    {
       if(size_type(last - end) < n)
          resize(n + (end - start));
-      register pointer result = end;
+      pointer result = end;
       end += n;
       return result;
    }