Add fcntl function support

[GabrielGanne]

In the project xdffileio, we only use the function fcntl with the commands F_GETFL and F_SETFL.
I propose that we write two functions in the mmlib to replace the use of fcntl:

fcntl(fd, F_GETFL) could be replaced by: int mm_getflags (int fd)
-> This function returns the value of the file status flag of fd on success, otherwise returns -1 and errno is set to the appropriate value.

fcntl(fd, F_SETFL, flags) could be replaced by: int mm_setflags(int fd, int flags)
-> Set the file descriptor flags of fd to the value specified by flags. Returns -1 in case of error and errno is set to the appropriate value, otherwise returns 0.