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

 # This file declares functions to install the kernel headers for mingw

 # Copyright 2009 Bart vdr. Meulen

 # Licensed under the GPL v2. See COPYING in the root of this package

 CT_DoKernelTupleValues() {

     CT_TARGET_KERNEL="mingw32"

     CT_TARGET_SYS=

 }

 do_kernel_get() {

     CT_GetFile "w32api-${CT_W32API_VERSION}-mingw32-src" \

         http://downloads.sourceforge.net/sourceforge/mingw

 }

 do_kernel_extract() {

     CT_Extract "w32api-${CT_W32API_VERSION}-mingw32-src"

 }

 do_kernel_headers() {

     CT_DoStep INFO "Installing kernel headers"

     mkdir -p "${CT_HEADERS_DIR}"

     cp -r ${CT_SRC_DIR}/w32api-${CT_W32API_VERSION}-mingw32-src/include/*   \

           ${CT_HEADERS_DIR}

     CT_EndStep

 }