Add back depot

Author: Sbozzolo

.buildkite/pipeline.yml

@@ -5,6 +5,7 @@ agents:
 
 env:
   JULIA_LOAD_PATH: "${JULIA_LOAD_PATH}:${BUILDKITE_BUILD_CHECKOUT_PATH}/.buildkite"
+  JULIA_DEPOT_PATH: "${BUILDKITE_BUILD_PATH}/${BUILDKITE_PIPELINE_SLUG}/depot/default"
   JULIA_MAX_NUM_PRECOMPILE_FILES: 100
   JULIA_CPU_TARGET: 'broadwell;skylake'
   JULIA_NVTX_CALLBACKS: gc