scripts: add option to start an interactive debug shell

Add an option that, when a command fails:
- starts an interactive shell with the failed command's environment
- attempts re-execution of the failed command, continues, or aborts
at user's whim.

Before starting the debug-shell, the backtrace is printed.
When exiting for an abort, the standard error message is printed.

Based on an idea and a patch from: Johannes Stezenbach <js@sig21.net>
http://sourceware.org/ml/crossgcc/2012-09/msg00144.html

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[yann.morin.1998@free.fr: integrate in the fault handler]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Johannes Stezenbach <js@sig21.net>
Patchwork-Id: 191571
Patchwork-Id: 191668

 # Configuration file for sstrip tool facility

 if OBSOLETE && ! BACKEND && ARCH_BINFMT_ELF

 comment "sstrip"

 config SSTRIP

     bool

     prompt "sstrip (OBSOLETE)"

     help

       The sstrip utility, to maximise the striping of ELF binaries

       (executables and libraries).

       Buildroot version, forked off the original from ELFkickers.

       This one is somewhat maintained by the buildroot guys.

       Supports big-endian systems.

       NOTE! Please read.

         sstrip is now deprecated in crosstool-NG, as it has a few

         shortcomings. For example: it breaks for PPC targets, it

         does not build on non-ELF hosts (eg. mingw32, MacOS-X...).

 endif