update xpu cmake for kunlun (PaddlePaddle#33328)

cmake/external/xpu.cmake

@@ -33,10 +33,7 @@ ELSE ()
   SET(XPU_XCCL_DIR_NAME "xccl-bdcentos_x86_64")
 ENDIF()
 
-IF(NOT XPU_BASE_URL)
-  SET(XPU_BASE_URL "https://baidu-kunlun-product.cdn.bcebos.com/KL-SDK/klsdk-dev/20210527")
-ENDIF()
-
+SET(XPU_BASE_URL "https://baidu-kunlun-product.cdn.bcebos.com/KL-SDK/klsdk-dev/20210527")
 SET(XPU_XRE_URL  "${XPU_BASE_URL}/${XPU_XRE_DIR_NAME}.tar.gz" CACHE STRING "" FORCE)
 SET(XPU_XDNN_URL "${XPU_BASE_URL}/${XPU_XDNN_DIR_NAME}.tar.gz" CACHE STRING "" FORCE)
 SET(XPU_XCCL_URL "${XPU_BASE_URL}/${XPU_XCCL_DIR_NAME}.tar.gz" CACHE STRING "" FORCE)
@@ -96,7 +93,11 @@ ELSE(WITH_XPU_BKCL)
   TARGET_LINK_LIBRARIES(xpulib ${XPU_API_LIB} ${XPU_RT_LIB})
 ENDIF(WITH_XPU_BKCL)
 
-ADD_DEPENDENCIES(xpulib ${XPU_PROJECT})
+if(NOT XPU_SDK_ROOT)
+  ADD_DEPENDENCIES(xpulib ${XPU_PROJECT})
+else()
+  ADD_CUSTOM_TARGET(extern_xpu DEPENDS xpulib)
+endif()
 
 # Ensure that xpu/api.h can be included without dependency errors.
 file(GENERATE OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/.xpu_headers_dummy.cc CONTENT "")