hwclock: size optimizations

libbb/time.c: new file, introducing monotonic_us()
pscan, traceroute, arping: use it instead of gettimeofday
ping, zcip: TODO

function                                             old     new   delta
monotonic_us                                           -      89     +89
find_pair                                            164     180     +16
.rodata                                           129747  129763     +16
refresh                                             1144    1152      +8
............
timeout                                                8       4      -4
static.start                                           8       4      -4
last                                                   8       4      -4
parse_conf                                          1303    1284     -19
time_main                                           1149    1124     -25
gettimeofday_us                                       39       -     -39
arping_main                                         2042    1969     -73
hwclock_main                                         594     501     -93
catcher                                              485     380    -105
traceroute_main                                     4300    4117    -183
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 8/11 up/down: 157/-562)        Total: -405 bytes

libbb/time.c

@@ -0,0 +1,32 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2007 Denis Vlasenko
+ *
+ * Licensed under GPL version 2, see file LICENSE in this tarball for details.
+ */
+
+#include "libbb.h"
+
+#if ENABLE_MONOTONIC_SYSCALL
+#include <sys/syscall.h>
+
+/* libc has incredibly messy way of doing this,
+ * typically requiring -lrt. We just skip all this mess */
+unsigned long long monotonic_us(void)
+{
+	struct timespec ts;
+	if (syscall(__NR_clock_gettime, CLOCK_MONOTONIC, &ts))
+		bb_error_msg_and_die("clock_gettime(MONOTONIC) failed");
+	return ts.tv_sec * 1000000ULL + ts.tv_nsec/1000;
+}
+#else
+unsigned long long monotonic_us(void)
+{
+	struct timeval tv;
+	if (gettimeofday(&tv, NULL))
+		bb_error_msg_and_die("gettimeofday failed");
+	return tv.tv_sec * 1000000ULL + tv_usec;
+}
+#endif