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>

 # Compute AVR32-specific values

 CT_DoArchTupleValues() {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}"

     # gcc ./configure flags

     CT_ARCH_WITH_ARCH=

     CT_ARCH_WITH_ABI=

     CT_ARCH_WITH_CPU=

     CT_ARCH_WITH_TUNE=

     CT_ARCH_WITH_FPU=

     CT_ARCH_WITH_FLOAT=

     CT_TARGET_SYS=none

 }