Linux: Correctly identify valid error codes

[syserr.errcat.objects]p4 specifies that
system_category().default_error_condition(ev) map to
error_condition(posv, generic_category()) if ev could map to a POSIX
errno.

Linux reserves up to and including 4095 for errno values, use this as a
bound.

This fixes syserr.errcat.objects/system_category.pass.cpp on Linux.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@209795 91177308-0d34-0410-b5e6-96231b3b80d8

src/ios.cpp

@@ -56,7 +56,9 @@ __iostream_category::message(int ev) const
     if (ev != static_cast<int>(io_errc::stream)
 #ifdef ELAST
         && ev <= ELAST
-#endif
+#elif defined(__linux__)
+        && ev <= 4095
+#endif  // ELAST
         )
         return __do_message::message(ev);
     return string("unspecified iostream_category error");