Modifications to run microROS on NuttX RTOS

Issue template

microROS on NuttX target runs correctly again, but there are some corrections required to correctly compile the example.

• Hardware description: nucelo-144 board
• RTOS: NuttX
• Installation type: microROS for NuttX (this example)
• Version or commit hash: galactic

Steps to reproduce the issue

The file micro_ros_src/src/rcutils/src/filesystem.c contains a redefinition of "DIR" (which is already defined in the dirent.h" file in NuTTX).

A test is required such

#ifdef DIR or #ifndef DIR....

Expected behavior

the nuttx application compile again

Actual behavior

There is the error about redefining DIR. To get the compilaton correctly I've commented the line

#ifdef RCUTILS_NO_FILESYSTEM
//typedef int DIR; <=======
#endif // _RCUTILS_NO_FILESYSTEM
typedef struct rcutils_dir_iter_state_t
{
#ifdef _WIN32
HANDLE handle;
WIN32_FIND_DATA data;
#else
DIR * dir;
#endif
} rcutils_dir_iter_state_t;

but it is not the correct solution.

Additional information

I've modified also the microros_main.c file in the microros/example_app

首先复现 NuttX 应用程序的编译，并结合 NuttX 的 dirent.h 中对 DIR 的定义检查 micro_ros_src/src/rcutils/src/filesystem.c。检查 RCUTILS_NO_FILESYSTEM 周围的条件处理，并验证示例无需重新定义 DIR 即可编译；issue 还提到了 microros/example_app/microros_main.c 中的更改，可能需要进行检查。