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 -uNpr gcc-4.2.1_orig/gcc/config/rs6000/darwin-ldouble.c gcc-4.2.1/gcc/config/rs6000/darwin-ldouble.c

--- gcc-4.2.1_orig/gcc/config/rs6000/darwin-ldouble.c	2007-03-05 11:54:00.000000000 -0500

+++ gcc-4.2.1/gcc/config/rs6000/darwin-ldouble.c	2008-01-31 17:51:24.000000000 -0500

@@ -70,6 +70,8 @@ Software Foundation, 51 Franklin Street,

    but GCC currently generates poor code when a union is used to turn

    a long double into a pair of doubles.  */

+#if defined (_SOFT_FLOAT) && defined (__LONG_DOUBLE_128__)

+

 long double __gcc_qadd (double, double, double, double);

 long double __gcc_qsub (double, double, double, double);

 long double __gcc_qmul (double, double, double, double);

@@ -219,8 +221,6 @@ __gcc_qdiv (double a, double b, double c

   return z.ldval;

 }

-#if defined (_SOFT_FLOAT) && defined (__LONG_DOUBLE_128__)

-

 long double __gcc_qneg (double, double);

 int __gcc_qeq (double, double, double, double);

 int __gcc_qne (double, double, double, double);