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

2008-04-28  Hiroki Kaminaga  <kaminaga@sm.sony.co.jp>

	[BZ 6740]

	nptl/sysdeps/powerpc/tcb-offsets.sym (PRIVATE_FUTEX_OFFSET):

	Guard sym definition with #ifndef __ASSUME_PRIVATE_FUTEX.

--- a/nptl/sysdeps/powerpc/tcb-offsets.sym

+++ b/nptl/sysdeps/powerpc/tcb-offsets.sym

@@ -15,4 +15,6 @@

 PID				thread_offsetof (pid)

 TID				thread_offsetof (tid)

 POINTER_GUARD			(offsetof (tcbhead_t, pointer_guard) - TLS_TCB_OFFSET - sizeof (tcbhead_t))

+#ifndef __ASSUME_PRIVATE_FUTEX

 PRIVATE_FUTEX_OFFSET		thread_offsetof (header.private_futex)

+#endif