enable incremental builds (#3292)

build.sh

@@ -104,6 +104,7 @@ pushd "$BUILD_DIR"
 # avoid the command failed and exits
 # and cmake will check some directories to determine whether some targets built
 make clean || true
+rm -rf external/arrow-install
 
 cmake -DCMAKE_BUILD_TYPE=$CBUILD_TYPE \
       -DCMAKE_RAY_LANG_JAVA=$RAY_BUILD_JAVA \

cmake/Modules/ArrowExternalProject.cmake

@@ -92,6 +92,7 @@ ExternalProject_Add(arrow_ep
   DEPENDS flatbuffers boost glog
   GIT_REPOSITORY ${arrow_URL}
   GIT_TAG ${arrow_TAG}
+  UPDATE_COMMAND ""
   ${ARROW_CONFIGURE}
   BUILD_BYPRODUCTS "${ARROW_SHARED_LIB}" "${ARROW_STATIC_LIB}")