Backport of this upstream commit:

commit 7f9d00341057eb80b43fa83956b8d7798b4dabea

Author: Roland McGrath <roland@hack.frob.com>

Date:   Tue Aug 27 11:09:33 2013 -0700

    Clean up h_errno declaration to use __thread unconditionally.

Adjusted for the IS_IN changes, which were applied upstream after this

commit (and downstream before its backport).

diff --git a/include/netdb.h b/include/netdb.h

index 3b24747fd5df6562..b6d7b90bbf8abd2e 100644

--- a/include/netdb.h

+++ b/include/netdb.h

@@ -5,17 +5,12 @@

 /* Macros for accessing h_errno from inside libc.  */

 # if IS_IN_LIB

 #  undef  h_errno

-#  ifdef _LIBC_REENTRANT

-#   include <tls.h>

-#   if IS_IN (libc)

-#    define h_errno __libc_h_errno

-#   else

-#    define h_errno h_errno	/* For #ifndef h_errno tests.  */

-#   endif

-extern __thread int h_errno attribute_tls_model_ie;

+#  if IS_IN (libc)

+#   define h_errno __libc_h_errno

 #  else

-extern int h_errno;

-#  endif	/* _LIBC_REENTRANT */

+#   define h_errno h_errno	/* For #ifndef h_errno tests.  */

+#  endif

+extern __thread int h_errno attribute_tls_model_ie;

 # endif /* IS_IN_LIB */

 # define __set_h_errno(x) (h_errno = (x))