Fix crypt snprintf namespace (bug 20829)

[Florian Weimer]

On 11/16/2016 08:05 PM, Joseph Myers wrote:

> 	[BZ #20829]
> 	* stdio-common/Versions (__snprintf): Add to version
> 	GLIBC_PRIVATE.
> 	* include/stdio.h (__snprintf): Use libc_hidden_proto.
> 	* stdio-common/snprintf.c (__snprintf): Use libc_hidden_def.
> 	* crypt/sha256-crypt.c (__sha256_crypt_r): Use __snprintf instead
> 	of snprintf.
> 	* crypt/sha512-crypt.c (__sha512_crypt_r): Likewise.

Looks good to me.  Thanks.

Florian