nptl: fix libc sigtimedwait

It seems that 57e8823548ad6e65d33b2153edeb18fb0edc20e6 removed completely
sigtimedwait symbol from libc which is wrong. I hope there is not too
many other things like this.

Apparently the libc_hidden_* macros actually make previously hidden
symbols visible globally (creates alias from __GI_* to *). This is
probably ancient confusion from times when gcc did not support
visibility attribute and hiding symbols was done using hacks like
this.

This also adds attribute_hidden to the internal __sigtimedwait for
nptl case.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: Austin Foxley <austinf@cetoncorp.com>

libc/sysdeps/linux/common/__rt_sigtimedwait.c

@@ -60,8 +60,8 @@ static int do_sigtimedwait(const sigset_t *set, siginfo_t *info,
 }
 
 /* Return any pending signal or wait for one for the given time.  */
-int __sigtimedwait(const sigset_t *set, siginfo_t *info,
-				   const struct timespec *timeout)
+int attribute_hidden __sigtimedwait(const sigset_t *set, siginfo_t *info,
+				    const struct timespec *timeout)
 {
 	if(SINGLE_THREAD_P)
 		return do_sigtimedwait(set, info, timeout);
@@ -102,3 +102,4 @@ int attribute_hidden __sigtimedwait(const sigset_t * set, siginfo_t * info,
 }
 #endif
 weak_alias(__sigtimedwait,sigtimedwait)
+libc_hidden_weak(sigtimedwait)