Update paddle_build.sh

Author: JiabinYang

paddle/scripts/paddle_build.sh

@@ -112,9 +112,9 @@ function cmake_gen() {
     if [ "$SYSTEM" == "Darwin" ]; then
         WITH_DISTRIBUTE=${WITH_DISTRIBUTE:-ON}
         WITH_AVX=${WITH_AVX:-ON}
-        INFERENCE_DEMO_INSTALL_DIR=${INFERENCE_DEMO_INSTALL_DIR}
+        INFERENCE_DEMO_INSTALL_DIR=${INFERENCE_DEMO_INSTALL_DIR:-~/.cache/inference_demo}
     else
-        INFERENCE_DEMO_INSTALL_DIR=${INFERENCE_DEMO_INSTALL_DIR=-/root/.cache/inference_demo}
+        INFERENCE_DEMO_INSTALL_DIR=${INFERENCE_DEMO_INSTALL_DIR:-/root/.cache/inference_demo}
     fi
 
     cat <<EOF