add legacy ftime function and sys/timeb.h

despite being marked legacy, this was specified by SUSv3 as part of
the XSI option; only the most recent version of the standard dropped
it. reportedly there's actual code using it.

include/sys/timeb.h

+#ifndef _SYS_TIMEB_H
+#define _SYS_TIMEB_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define __NEED_time_t
+
+#include <bits/alltypes.h>
+
+struct timeb {
+	time_t time;
+	unsigned short millitm;
+	short timezone, dstflag;
+};
+
+int ftime(struct timeb *);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

src/time/ftime.c

+#include <sys/timeb.h>
+#include <time.h>
+
+int ftime(struct timeb *tp)
+{
+	struct timespec ts;
+	clock_gettime(CLOCK_REALTIME, &ts);
+	tp->time = ts.tv_sec;
+	tp->millitm = ts.tv_nsec / 1000000;
+	tp->timezone = tp->dstflag = 0;
+	return 0;
+}