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

 --- glibc-2.7/sysdeps/unix/sysv/linux/kernel-features.h	2007-08-14 06:21:09.000000000 +0300

 +++ glibc-2.7/sysdeps/unix/sysv/linux/kernel-features.h.new	2008-07-23 07:05:20.000000000 +0300

 @@ -449,8 +449,7 @@

     and on Alpha just after 2.6.22-rc1.  */

  #if __LINUX_KERNEL_VERSION >= 0x020611 \

      && ((!defined __sh__ && !defined __alpha__) \

 -	|| (__LINUX_KERNEL_VERSION >= 0x020613 && defined __sh__) \

 -	|| (__LINUX_KERNEL_VERSION >= 0x020617 && defined __alpha__))

 +	|| (__LINUX_KERNEL_VERSION >= 0x020613 && defined __sh__))

  # define __ASSUME_ATFCTS	1

  #endif