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>

 2008-06-07  Mike Frysinger  <vapier@gentoo.org>

 	* sysdeps/unix/sysv/linux/alpha/sys/user.h: Copy page.h definitions

 	from the kernel header to sys/user.h and remove the #include of

 	sys/user.h.

 --- a/sysdeps/unix/sysv/linux/alpha/sys/user.h

 +++ b/sysdeps/unix/sysv/linux/alpha/sys/user.h

 @@ -23,7 +23,6 @@

     only. Don't read too much into it. Don't use it for anything other

     than gdb/strace unless you know what you are doing. */

 -#include <asm/page.h>

  #include <asm/reg.h>

  struct user

 @@ -41,6 +40,9 @@ struct user

    char u_comm[32];				/* user command name */

  };

 +#define PAGE_SHIFT		13

 +#define PAGE_SIZE		(1 << PAGE_SHIFT)

 +#define PAGE_MASK		(~(PAGE_SIZE-1))

  #define NBPG			PAGE_SIZE

  #define UPAGES			1

  #define HOST_TEXT_START_ADDR	(u.start_code)