kernel_decode_stack: Set ARCH in environment for decodecode

The decodecode script is called from the decode_stacktrace.sh script and
it needs to have ARCH set so it knows which architecture to dump the
code in assembly form as. Otherwise the ARCH comes from uname -m, which
doesn't work well when running this for an ARM/ARM64 crash on an x86
machine.

BUG=None
TEST=kernel_decode_stack -b trogdor; see assembly make sense

Change-Id: I902a4a1a766e4beecbc382367b9ee42fbda3dd0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/3309762
Tested-by: Stephen Boyd <swboyd@chromium.org>
Auto-Submit: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Pi-Hsun Shih <pihsun@chromium.org>
Commit-Queue: Pi-Hsun Shih <pihsun@chromium.org>
diff --git a/contrib/kernel_decode_stack b/contrib/kernel_decode_stack
index 8ef0631..f4b09db 100755
--- a/contrib/kernel_decode_stack
+++ b/contrib/kernel_decode_stack
@@ -64,7 +64,7 @@
       head -1 |
       sed 's|\(.*\)/include/linux/compiler.h:$|\1|')
 
-  CROSS_COMPILE="${cross}-" \
+  ARCH=${kernel_arch} CROSS_COMPILE="${cross}-" \
     "${SRC_ROOT}/third_party/kernel/upstream/scripts/decode_stacktrace.sh" \
     "/build/${board}/usr/lib/debug/boot/vmlinux" \
     "${kernel_source_path}" \