Fix qsort_r namespace (bug 17571).

Fix qsort_r namespace (bug 17571).

qsort_r is defined in the same file as qsort, but is not an ISO C
function, so should be a weak alias for __qsort_r.  The uses in
getaddrinfo should also call __qsort_r, since getaddrinfo is a POSIX
function and qsort_r isn't.  This patch implements this.  Because nscd
uses the getaddrinfo sources outside libc, as do the tst-rfc3484
tests, a #define of __qsort_r to qsort_r is added there alongside the
similar defines for other libc-internal symbols used in getaddrinfo.

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch).

	[BZ #17571]
	* stdlib/msort.c (qsort_r): Rename to __qsort_r and define as weak
	alias of __qsort_r.
	(qsort): Call __qsort_r instead of qsort_r.
	* include/stdlib.h (qsort_r): Do not call libc_hidden_proto.
	(__qsort_r): Declare.  Call libc_hidden_proto.
	* sysdeps/posix/getaddrinfo.c (getaddrinfo): Call __qsort_r
	instead of qsort_r.
	* nscd/gai.c (__qsort_r): Define to qsort_r.
	* posix/tst-rfc3484.c (__qsort_r): Likewise.
	* posix/tst-rfc3484-2.c (__qsort_r): Likewise.
	* posix/tst-rfc3484-3.c (__qsort_r): Likewise.