cmake:bugfix fix cmake CPP options get NULL in add_romfs

CMake Error at cmake/nuttx_add_romfs.cmake:60 (string):
  string sub-command REPLACE requires at least four arguments.
Call Stack (most recent call first):
  boards/sim/sim/sim/src/CMakeLists.txt:68 (nuttx_add_romfs)

Signed-off-by: xuxin19 <xuxin19@xiaomi.com>

cmake/nuttx_add_romfs.cmake

@@ -59,14 +59,28 @@ function(nuttx_add_romfs)
     message(FATAL_ERROR "Either PATH or FILES must be specified")
   endif()
 
+  get_directory_property(TOOLCHAIN_DIR_FLAGS DIRECTORY ${CMAKE_SOURCE_DIR}
+                                                       COMPILE_OPTIONS)
+
+  set(ROMFS_CMAKE_C_FLAGS "")
+  foreach(FLAG ${TOOLCHAIN_DIR_FLAGS})
+    if(NOT FLAG MATCHES "^\\$<.*>$")
+      list(APPEND ROMFS_CMAKE_C_FLAGS ${FLAG})
+    else()
+      string(REGEX MATCH "\\$<\\$<COMPILE_LANGUAGE:C>:(.*)>" matched ${FLAG})
+      if(matched)
+        list(APPEND ROMFS_CMAKE_C_FLAGS ${CMAKE_MATCH_1})
+      endif()
+    endif()
+  endforeach()
+
   foreach(rcsrc ${RCSRCS})
     get_filename_component(rcpath ${rcsrc} DIRECTORY)
-    separate_arguments(CMAKE_C_FLAG_ARGS NATIVE_COMMAND ${CMAKE_C_FLAGS})
     add_custom_command(
       OUTPUT ${rcsrc}
       COMMAND ${CMAKE_COMMAND} -E make_directory ${rcpath}
       COMMAND
-        ${CMAKE_C_COMPILER} ${CMAKE_C_FLAG_ARGS} -E -P -x c
+        ${CMAKE_C_COMPILER} ${ROMFS_CMAKE_C_FLAGS} -E -P -x c
         -I${CMAKE_BINARY_DIR}/include ${CMAKE_CURRENT_SOURCE_DIR}/${rcsrc} >
         ${rcsrc}
       DEPENDS nuttx_context ${CMAKE_CURRENT_SOURCE_DIR}/${rcsrc})