uuid: use CLOCK_REALTIME if CLOCK_MONOTONIC not available

Older versions of glibc may not have CLOCK_MONOTONIC, this is certainly the
case for the 2.3.2 based terastation libc.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>

uuid.c

@@ -47,6 +47,10 @@ static uint32_t clock_seq;
 static const uint32_t clock_seq_max = 0x3fff; /* 14 bits */
 static int clock_seq_initialized;
 
+#ifndef CLOCK_MONOTONIC
+#define CLOCK_MONOTONIC CLOCK_REALTIME
+#endif
+
 unsigned long long
 monotonic_us(void)
 {