Fix Kokoro ASAN builds

The VM has been updated to Kokoro 14.04, and now the docker instance
requires escalated privileges in order to run some sanitizer builds.

Change-Id: Icebbb1597dcdb67a854cb61ff7b0c0c11952b7f2
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/71921
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

kokoro/linux/build.sh

@@ -31,7 +31,9 @@ else
 fi
 
 
+# --privileged is required for some sanitizer builds, as they seem to require PTRACE privileges
 docker run --rm -i \
+  --privileged \
   --volume "${ROOT_DIR}:${ROOT_DIR}" \
   --volume "${TMP_DIR}:/src" \
   --volume "${KOKORO_ARTIFACTS_DIR}:/mnt/artifacts" \