Create hidden aliases for non-libc syscalls automatically.

Create hidden aliases for non-libc syscalls automatically.

The syscall wrappers mechanism automatically creates hidden aliases
for syscalls with libc_hidden_def / libc_hidden_weak.  The use of
libc_hidden_* has the side-effect that for syscall wrappers in
non-libc libraries those aliases are not created.  In turn, this means
that three mq_* syscalls in sysdeps/unix/sysv/linux/syscalls.list list
the __GI_* names explicitly.

The use of libc_hidden_* dates back to the original introduction of
that support in

2002-08-03  Roland McGrath  <roland@redhat.com>

        * sysdeps/unix/make-syscalls.sh: Generate libc_hidden_def or
        libc_hidden_weak for every system call symbol defined.

(predating the non-libc syscalls in question) and I see no reason for
excluding non-libc syscalls.  This patch changes the code to use
hidden_def / hidden_weak (via a wrapper syscall_hidden_def in the case
where the argument is itself a macro, so that the argument gets
expanded before concatenation with __GI_), so avoiding the need to
specify the hidden aliases explicitly in this case.

Tested for x86_64 and x86 (testsuite, and that disassembly of
installed stripped shared libraries is unchanged by the patch; the
mq_* symbols change from weak to strong, which is of no significance
and two of them will shortly change back to weak as part of a fix for
bug 18545).

	* sysdeps/unix/make-syscalls.sh (emit_weak_aliases): Use
	hidden_def and hidden_weak instead of libc_hidden_def and
	libc_hidden_weak.
	(top level): Refer to hidden_def in comment.
	* sysdeps/unix/syscall-template.S (syscall_hidden_def): New
	macro.  Use it instead of libc_hidden_def.
	* sysdeps/unix/sysv/linux/syscalls.list (mq_timedsend): Do not
	specify __GI_* name explicitly.
	(mq_timedreceive): Likewise.
	(mq_setattr): Likewise.