Melis link library error: undefined reference to'_close','_fstat','_isatty','_lseek','_read', etc.

When linking libraries in melis sdk, the following error is sometimes reported:

At this point it is due to call a number of functions in the library system's file, but these systems function can not find the corresponding C library caused, for example printf(), assert(), open(), close(), read(), write()and so on.

Modify these functions to the corresponding functions in the C library used.