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://sourceware.org/ml/binutils/2007-07/msg00401.html

http://sourceware.org/bugzilla/show_bug.cgi?id=4970

diff -durN binutils-2.20.1.orig/configure binutils-2.20.1/configure

--- binutils-2.20.1.orig/configure	2010-03-03 14:59:02.000000000 +0100

+++ binutils-2.20.1/configure	2010-08-17 19:32:05.000000000 +0200

@@ -6466,6 +6466,7 @@

   *-*-mingw* | *-*-cygwin ) RPATH_ENVVAR=PATH ;;

   *) RPATH_ENVVAR=LD_LIBRARY_PATH ;;

 esac

+RPATH_ENVVAR="cant_touch_this_nah_nah_nah"

 # On systems where the dynamic library environment variable is PATH,

 # gcc/ will put dynamic libraries into a subdirectory to avoid adding