scripts: fix catching failures

POSIX 1003.1-2008 does not say whether "set -e" should catch a sub-shell
that exits with !0 (it has a list of conditions to catch, but no list of
conditions not to catch, and this situation is not listed).

bash-3 does not catch such a failure, but bash-4 does. That why, on my
Squeeze system I did not see the issue, while Thomas did on is Lenny chroot.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 --- gcc-4.0.0/boehm-gc/include/gc.h-orig	2005-04-28 22:28:57.000000000 -0500

 +++ gcc-4.0.0/boehm-gc/include/gc.h	2005-04-28 22:30:38.000000000 -0500

 @@ -500,7 +500,7 @@

  #ifdef __linux__

  # include <features.h>

  # if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1 || __GLIBC__ > 2) \

 -     && !defined(__ia64__)

 +     && !defined(__ia64__) && !defined(__UCLIBC__)

  #   ifndef GC_HAVE_BUILTIN_BACKTRACE

  #     define GC_HAVE_BUILTIN_BACKTRACE

  #   endif