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

@@ -0,0 +1,22 @@
+#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