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>

This is the README for crosstool-NG

Crosstool-NG follows the autoconf dance. So, to get you

kick-started, just run:

  ./configure --help

You will find the documentation in the directory 'docs'.

Here is a quick overview of what you'll find there:

  0 - Table of content

  1 - Introduction

  2 - Installing crosstool-NG

  3 - Configuring a toolchain

  4 - Building the toolchain

  5 - Using the toolchain

  6 - Toolchain types

  7 - Contributing

  8 - Internals

  A - Credits

  B - Known issues

  C - Misc. tutorials

You can also point your browser at:

  http://ymorin.is-a-geek.org/projects/crosstool

Aloha!