scripts/libc: do not build add-ons by default

Currently, no --enable-add-ons option is passed to libc configure when
"$(do_libc_add_ons_list ,)" is empty, which makes configure automatically search
for present add-ons. In that case, all present add-ons are built, although
no add-on was selected by the user in the config. Moreover, this can make the
configure fail if some non-standard add-ons like eglibc-localedef are present.

This behavior also leads to an inconsistency from a user point of view between
the following cases:
- LIBC_ADDONS_LIST="", LIBC_GLIBC_USE_PORTS=n and THREADS="none" in the config,
which makes "$(do_libc_add_ons_list ,)" return "", so all present add-ons
are built.
- LIBC_ADDONS_LIST="", LIBC_GLIBC_USE_PORTS=n and THREADS!="none" in the
config, which makes "$(do_libc_add_ons_list ,)" return the add-on supporting
the chosen threading implementation, e.g. "nptl", so only this add-on is
built.

This patch disables the building of all add-ons in that case.

It is still possible to build all present add-ons by adding --enable-add-ons to
LIBC_GLIBC_EXTRA_CONFIG_ARRAY.

Signed-off-by: "Benoît THÉBAUDEAU" <benoit.thebaudeau@advansee.com>

--- strace-orig/file.c	2008/05/20 04:56:18	1.92

+++ strace/file.c	2008/08/01 01:13:10	1.93

@@ -28,21 +28,22 @@

  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  *

- *	$Id: file.c,v 1.92 2008/05/20 04:56:18 roland Exp $

+ *	$Id: file.c,v 1.93 2008/08/01 01:13:10 roland Exp $

  */

 #include "defs.h"

 #include <dirent.h>

+

 #ifdef LINUX

-#define dirent kernel_dirent

-#define dirent64 kernel_dirent64

-#include <linux/types.h>

-#include <linux/dirent.h>

-#undef dirent

-#undef dirent64

+struct kernel_dirent {

+	unsigned long   d_ino;

+	unsigned long   d_off;

+	unsigned short  d_reclen;

+	char            d_name[1];

+};

 #else

-#define kernel_dirent dirent

+# define kernel_dirent dirent

 #endif

 #ifdef LINUX