Partial backport of this upstream commit:

commit 9acacaa02f3b75fddc07a56f3d848df45281a5de

Author: Joseph Myers <joseph@codesourcery.com>

Date:   Fri Jun 12 10:10:18 2015 +0000

    Fix h_errno namespace (bug 18520).

The linknamespace test changes in conform/Makefile are not included here

because glibc 2.17 did not have these tests.

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

index b6d7b90bbf8abd2e..6a6dca9ef57aaa37 100644

--- a/include/netdb.h

+++ b/include/netdb.h

@@ -8,7 +8,7 @@

 #  if IS_IN (libc)

 #   define h_errno __libc_h_errno

 #  else

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

+#   define h_errno __h_errno

 #  endif

 extern __thread int h_errno attribute_tls_model_ie;

 # endif /* IS_IN_LIB */

diff --git a/inet/herrno.c b/inet/herrno.c

index 1802d0e00563839a..0cd84445190728b3 100644

--- a/inet/herrno.c

+++ b/inet/herrno.c

@@ -24,7 +24,7 @@

 /* We need to have the error status variable of the resolver

    accessible in the libc.  */

-__thread int h_errno;

-extern __thread int __libc_h_errno __attribute__ ((alias ("h_errno")))

+__thread int __h_errno;

+extern __thread int __libc_h_errno __attribute__ ((alias ("__h_errno")))

   attribute_hidden;

 #define h_errno __libc_h_errno

diff --git a/nptl/herrno.c b/nptl/herrno.c

index c0488e4f6754873f..5056e3df88211123 100644

--- a/nptl/herrno.c

+++ b/nptl/herrno.c

@@ -23,12 +23,12 @@

 /* We need to have the error status variable of the resolver

    accessible in the libc.  */

-extern __thread int h_errno;

+extern __thread int __h_errno;

 /* When threaded, h_errno may be a per-thread variable.  */

 int *

 __h_errno_location (void)

 {

-  return &h_errno;

+  return &__h_errno;

 }

diff --git a/resolv/Versions b/resolv/Versions

index 93faf1e2f5faac79..152ef3f68f9a8b48 100644

--- a/resolv/Versions

+++ b/resolv/Versions

@@ -26,7 +26,7 @@ libc {

   GLIBC_PRIVATE {

     __gai_sigqueue;

-    h_errno; __resp;

+    __h_errno; __resp;

     __res_maybe_init; __res_iclose;

   }