Fix build error on Windows (PaddlePaddle#653)

Author: jiangjiajun

CMakeLists.txt

@@ -369,7 +369,9 @@ if(ENABLE_TRT_BACKEND)
     message(STATUS "Copying ${TRT_DIRECTORY}/lib to ${CMAKE_CURRENT_BINARY_DIR}/third_libs/install/tensorrt/lib ...")
     execute_process(COMMAND ${Python_EXECUTABLE} ${PROJECT_SOURCE_DIR}/scripts/copy_directory.py ${TRT_DIRECTORY}/lib ${CMAKE_CURRENT_BINARY_DIR}/third_libs/install/tensorrt/lib)
     file(GLOB_RECURSE TRT_STAIC_LIBS ${CMAKE_CURRENT_BINARY_DIR}/third_libs/install/tensorrt/lib/*.a)
-    file(REMOVE ${TRT_STAIC_LIBS})
+    if(TRT_STATIC_LIBS)
+      file(REMOVE ${TRT_STAIC_LIBS})
+    endif()
     if(UNIX AND (NOT APPLE) AND (NOT ANDROID))
       execute_process(COMMAND sh -c "ls *.so*" WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/third_libs/install/tensorrt/lib
 	      COMMAND sh -c "xargs ${PATCHELF_EXE} --set-rpath '$ORIGIN'" WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/third_libs/install/tensorrt/lib