Fix Apple deployment env and refresh NSC caches

Apple/NetworkExtension/libburrow/build-rust.sh

@@ -88,7 +88,19 @@ for VAR_NAME in HOME CARGO_HOME CARGO_TARGET_DIR RUSTUP_HOME RUSTC_WRAPPER SCCAC
     fi
 done
 EFFECTIVE_CARGO_TARGET_DIR="${CARGO_TARGET_DIR:-${CONFIGURATION_TEMP_DIR}/target}"
-env -i PATH="$CARGO_PATH" PROTOC="$PROTOC" CARGO_TARGET_DIR="${EFFECTIVE_CARGO_TARGET_DIR}" IPHONEOS_DEPLOYMENT_TARGET="$IPHONEOS_DEPLOYMENT_TARGET" MACOSX_DEPLOYMENT_TARGET="$MACOSX_DEPLOYMENT_TARGET" "${EXTRA_ENV[@]}" cargo build "${CARGO_ARGS[@]}"
+BUILD_ENV=(
+    "PATH=$CARGO_PATH"
+    "PROTOC=$PROTOC"
+    "CARGO_TARGET_DIR=${EFFECTIVE_CARGO_TARGET_DIR}"
+    "${EXTRA_ENV[@]}"
+)
+if [[ -n "${IPHONEOS_DEPLOYMENT_TARGET:-}" ]]; then
+    BUILD_ENV+=("IPHONEOS_DEPLOYMENT_TARGET=${IPHONEOS_DEPLOYMENT_TARGET}")
+fi
+if [[ -n "${MACOSX_DEPLOYMENT_TARGET:-}" ]]; then
+    BUILD_ENV+=("MACOSX_DEPLOYMENT_TARGET=${MACOSX_DEPLOYMENT_TARGET}")
+fi
+env -i "${BUILD_ENV[@]}" cargo build "${CARGO_ARGS[@]}"
 
 mkdir -p "${BUILT_PRODUCTS_DIR}"