package/gcc: backport xtensa trap pattern for 5.x

package/gcc: backport xtensa trap pattern for 5.x

gcc 5.x uses trap pattern extensively to mark locations where program
execution should never get. Default pattern implementation emits a call
to 'abort' function. This function however is not always available, e.g.
it's not available for the libc dynamic linker. Backport implementation
of the trap pattern for xtensa that does not result in a call to
'abort'.

Fixes:
  http://autobuild.buildroot.net/results/0fbcc4475545904bf88f25a3bdf3ee552bf4960e
  http://autobuild.buildroot.net/results/cb7f5bdfac615d774f3bcd1b802f8d74460bc557
  http://autobuild.buildroot.net/results/cf3dc9ae4f74ff28b285f1a862b71d96384d7651

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>