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>

 Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> wrote:

 I tried to use crosstool-ng to generate a toolchain for Linux on big

 endian arm with recent versions of gcc, glibc, etc... but had a few

 problems.

 It appears that the gcc patch (for gcc 4.2.x)

 for big-endian arm (240-arm-bigendian.patch) lacks the change attached

 to this mail as 240-arm-bigendian2.patch.

 --- gcc-4.2.4/gcc/config/arm/bpabi.h~	2007-09-01 17:28:30.000000000 +0200

 +++ gcc-4.2.4/gcc/config/arm/bpabi.h	2009-01-05 19:19:10.000000000 +0100

 @@ -32,9 +32,19 @@

  #undef FPUTYPE_DEFAULT

  #define FPUTYPE_DEFAULT FPUTYPE_VFP

 +/*

 + * 'config.gcc' defines TARGET_BIG_ENDIAN_DEFAULT as 1 for arm*b-*

 + * (big endian) configurations.

 + */

 +#if TARGET_BIG_ENDIAN_DEFAULT

 +#define TARGET_ENDIAN_DEFAULT MASK_BIG_END

 +#else

 +#define TARGET_ENDIAN_DEFAULT 0

 +#endif

 +

  /* EABI targets should enable interworking by default.  */

  #undef TARGET_DEFAULT

 -#define TARGET_DEFAULT MASK_INTERWORK

 +#define TARGET_DEFAULT (MASK_INTERWORK | TARGET_ENDIAN_DEFAULT)

  /* The ARM BPABI functions return a boolean; they use no special

     calling convention.  */