vfs: use sys/dirent.h from newlib
vfs: use sys/dirent.h from newlib

The dirent.h shipped with the risc-v compiler lacks `extern "C"`
declartion and causes linkage declartion conflict when included in C++
files. Use the dirent.h from newlib only to avoid this issue.

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf