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>

http://sources.redhat.com/ml/binutils/2004-04/msg00665.html

fixes building on some architectures (like m68k/arm/cris/etc...) because

it does the right thing

diff -durN glibc-2.12.1.orig/include/libc-symbols.h glibc-2.12.1/include/libc-symbols.h

--- glibc-2.12.1.orig/include/libc-symbols.h	2009-03-14 00:51:46.000000000 +0100

+++ glibc-2.12.1/include/libc-symbols.h	2009-11-13 00:50:07.000000000 +0100

@@ -239,12 +239,12 @@

 #  define __make_section_unallocated(section_string)

 # endif

-/* Tacking on "\n\t#" to the section name makes gcc put it's bogus

+/* Tacking on "\n#APP\n\t#" to the section name makes gcc put it's bogus

    section attributes on what looks like a comment to the assembler.  */

 # ifdef HAVE_SECTION_QUOTES

-#  define __sec_comment "\"\n\t#\""

+#  define __sec_comment "\"\n#APP\n\t#\""

 # else

-#  define __sec_comment "\n\t#"

+#  define __sec_comment "\n#APP\n\t#"

 # endif

 # define link_warning(symbol, msg) \

   __make_section_unallocated (".gnu.warning." #symbol) \