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>

 diff -durN glibc-2.7.orig/sysdeps/unix/sysv/linux/sh/sys/procfs.h glibc-2.7/sysdeps/unix/sysv/linux/sh/sys/procfs.h

 --- glibc-2.7.orig/sysdeps/unix/sysv/linux/sh/sys/procfs.h	2008-10-22 21:23:32.000000000 +0200

 +++ glibc-2.7/sysdeps/unix/sysv/linux/sh/sys/procfs.h	2008-10-22 21:41:54.000000000 +0200

 @@ -29,6 +29,7 @@

  #include <sys/types.h>

  #include <sys/ucontext.h>

  #include <sys/user.h>

 +#include <asm/ptrace.h>

  __BEGIN_DECLS

 diff -durN glibc-2.7.orig/sysdeps/unix/sysv/linux/sh/sys/user.h glibc-2.7/sysdeps/unix/sysv/linux/sh/sys/user.h

 --- glibc-2.7.orig/sysdeps/unix/sysv/linux/sh/sys/user.h	2008-10-22 21:23:32.000000000 +0200

 +++ glibc-2.7/sysdeps/unix/sysv/linux/sh/sys/user.h	2008-10-22 21:33:34.000000000 +0200

 @@ -21,8 +21,6 @@

  #include <features.h>

 -#include <asm/user.h>

 -

  #undef start_thread

  #endif  /* sys/user.h */