system/flatbuffers: fix patch flow of flatbuffers

Applying patch to flatbuffers
patching file '<'
Hunk #1 FAILED at 1.
1 out of 1 hunk FAILED -- saving rejects to file '<.rej'
patching file '<'
Hunk #1 FAILED at 39.
1 out of 1 hunk FAILED -- saving rejects to file '<.rej'
patching file '<'
Hunk #1 FAILED at 495.
1 out of 1 hunk FAILED -- saving rejects to file '<.rej'
patching file '<'
Hunk #1 FAILED at 23.
1 out of 1 hunk FAILED -- saving rejects to file '<.rej'
patch: **** Can't reopen file '<' : No such file or directory
-- Configuring done (12.8s)
-- Generating done (0.3s)

Signed-off-by: chao an <anchao@lixiang.com>

Author: anchao

system/flatbuffers/CMakeLists.txt

@@ -33,21 +33,15 @@ if(CONFIG_SYSTEM_FLATBUFFERS)
       flatbuffers_fetch
       URL ${FLATBUFFERS_URL} SOURCE_DIR ${FLATBUFFERS_DIR} BINARY_DIR
           ${CMAKE_BINARY_DIR}/apps/math/flatbuffers/flatbuffers
+      PATCH_COMMAND patch -d ${FLATBUFFERS_DIR} -p1 <
+                    ${CMAKE_CURRENT_LIST_DIR}/flatbuffers.patch
       DOWNLOAD_NO_PROGRESS true
       TIMEOUT 30)
 
     FetchContent_GetProperties(flatbuffers_fetch)
 
     if(NOT flatbuffers_fetch_POPULATED)
       FetchContent_Populate(flatbuffers_fetch)
-
-      # Apply the patch after fetching the content
-      execute_process(
-        COMMAND ${CMAKE_COMMAND} -E echo "Applying patch to flatbuffers"
-        WORKING_DIRECTORY ${CMAKE_CURRENT_LIST_DIR})
-
-      execute_process(COMMAND patch -d ${FLATBUFFERS_DIR} -p1 <
-                              ${CMAKE_CURRENT_LIST_DIR}/flatbuffers.patch)
     endif()
   endif()