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/internal-signals.h

@@ -23,6 +23,7 @@
 #include <sigsetops.h>
 #include <stdbool.h>
 #include <limits.h>
+#include <stddef.h>
 #include <sysdep.h>
 
 /* The signal used for asynchronous cancelation.  */