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

Original patch from Gentoo.

-= BEGIN original header =-

-= END original header =-

diff -durN uClibc-0.9.30.orig/libc/sysdeps/linux/arm/bits/uClibc_arch_features.h uClibc-0.9.30/libc/sysdeps/linux/arm/bits/uClibc_arch_features.h

--- uClibc-0.9.30.orig/libc/sysdeps/linux/arm/bits/uClibc_arch_features.h	2008-09-25 10:50:56.000000000 +0200

+++ uClibc-0.9.30/libc/sysdeps/linux/arm/bits/uClibc_arch_features.h	2009-02-07 09:57:59.000000000 +0100

@@ -39,4 +39,8 @@

 /* define if target supports IEEE signed zero floats */

 #define __UCLIBC_HAVE_SIGNED_ZERO__

+#ifdef __ARM_EABI__

+# define __UCLIBC_TRUNCATE64_HAS_4_ARGS__

+#endif

+

 #endif /* _BITS_UCLIBC_ARCH_FEATURES_H */