Fix __get_nprocs fgets_unlocked namespace (bug 17582).

__get_nprocs is called from malloc code, but calls fgets_unlocked,
which is not an ISO C or POSIX function.  This patch fixes it to call
a new __fgets_unlocked name instead.

Note: there are various other uses of fgets_unlocked in glibc's
libraries, and I haven't yet investigated which others might also be
problematic (called directly or indirectly from standard functions)
and so need to change to use __fgets_unlocked.

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

	[BZ #17582]
	* libio/iofgets.c [weak_alias && !_IO_MTSAFE_IO]
	(__fgets_unlocked): Add alias of _IO_fgets.  Use libc_hidden_def.
	* libio/iofgets_u.c (fgets_unlocked): Rename to __fgets_unlocked
	and define as weak alias of __fgets_unlocked.  Use
	libc_hidden_weak.
	(__fgets_unlocked): Use libc_hidden_def.
	* include/stdio.h (__fgets_unlocked): Declare.  Use
	libc_hidden_proto.
	* sysdeps/unix/sysv/linux/getsysstats.c (phys_pages_info): Use
	__fgets_unlocked instead of fgets_unlocked.
	* sysdeps/unix/sysv/linux/alpha/getsysstats.c
	(GET_NPROCS_CONF_PARSER): Likewise.
	* sysdeps/unix/sysv/linux/sparc/getsysstats.c
	(GET_NPROCS_CONF_PARSER): Likewise.

sysdeps/unix/sysv/linux/getsysstats.c

@@ -299,7 +299,7 @@ phys_pages_info (const char *format)
 	 string "processor".  We don't have to fear extremely long
 	 lines since the kernel will not generate them.  8192
 	 bytes are really enough.  */
-      while (fgets_unlocked (buffer, sizeof buffer, fp) != NULL)
+      while (__fgets_unlocked (buffer, sizeof buffer, fp) != NULL)
 	if (sscanf (buffer, format, &result) == 1)
 	  {
 	    result /= (__getpagesize () / 1024);