Remove tls.h inclusion from internal errno.h

The tls.h inclusion is not really required and limits possible
definition on more arch specific headers.

This is a cleanup to allow inline functions on sysdep.h, more
specifically on i386 and ia64 which requires to access some tls
definitions its own.

No semantic changes expected, checked with a build against all
affected ABIs.

sysdeps/unix/sysv/linux/generic/dup2.c

@@ -16,10 +16,9 @@
    License along with the GNU C Library.  If not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
 #include <fcntl.h>
-#include <limits.h>
 #include <unistd.h>
+#include <sysdep.h>
 
 /* Duplicate FD to FD2, closing the old FD2 and making FD2 be
    open the same file as FD is.  Return FD2 or -1.  */