Add POSIX prototypes for time functions, to allow external code to build

more easily within gPXE.

Note that we don't have function bodies for these functions yet.

src/include/sys/time.h

@@ -0,0 +1,20 @@
+#ifndef _SYS_TIME_H
+#define _SYS_TIME_H
+
+#include <time.h>
+
+typedef unsigned long suseconds_t;
+
+struct timeval {
+	time_t tv_sec;		/* seconds */
+	suseconds_t tv_usec;	/* microseconds */
+};
+
+struct timezone {
+	int tz_minuteswest;	/* minutes W of Greenwich */
+	int tz_dsttime;		/* type of dst correction */
+};
+
+extern int gettimeofday ( struct timeval *tv, struct timezone *tz );
+
+#endif /* _SYS_TIME_H */