cc/gcc: implement default for core options

cc/gcc: fix headers copy for core static

complibs/mpfr: update to latest version

libc/uClibc: apply the threading model to the configuration

The threading model shall be be set in the .config file.
Also, offer the choice between 'old/stable' and 'new' linuxthreads.

config: add support for a second part of the generated choices

Some components have configuration options that can depend on
generic options, so they should go below those.

uClibc for example:
- has its own options (wchar...)
- uses the generic options (threads...)
- if linuxthreads chosen, offers two impls

So we need to be able to split the components options in 2,
one part that is above the generic options, and one part that
ends up below the generic options.

docs: update credtis, point to the repository log

The docs/CREDITS file dates back to the SVN repository.
Now that we use Mercurial, the repository stores appropriate
authorship for each commit. Say so in the CREDITS.

kernel/linux: update to latest versions

kconfig/lxdialog: more portable and use ncurses from macports on MacOS

check-lxdialog.sh now correctly tests for ncurses and is a bit more portable.
On Darwin it uses the ncurses from macports.

cc/gcc: Make usage of --enable-target-optspace configurable

Optionally configure to compile gcc-internal libs with -Os.

yann.morin.1998@anciens.enib.fr:
Rename the config options, it is in the GCC /namespace/.

docs: Provide new Readme for MacOS

Short README for usage of ct-ng under MacOS.
Remove obsolete MacOS-X.txt

yann.morin.1998@anciens.enib.fr:
Make it 80-columns clean, plus a few fixes