One alternative is to create a C function stime and link this C file with flang.
-- stime.c ---
#include <time.h>
int stime(const time_t *t)
{
struct timespec ts = {};
ts.tv_sec = *t;
return clock_settime(CLOCK_REALTIME, &ts); }
$ flang test.f90 stime.c
Please let us know if above helps.