Use urandom to get random seed

When available use /dev/urandom to get the random seem. This will lower the probability
of collisions.

On other systems it will fallback to the old methods.

Passes bootstrap + testsuite on x86_64. Ok?

gcc/:

2011-09-26   Andi Kleen <ak@linux.intel.com>

	* toplev.c (init_local_tick): Try reading random seed from /dev/urandom

From-SVN: r179348

gcc/ChangeLog

 2011-09-26   Andi Kleen <ak@linux.intel.com>
 
+	* toplev.c (init_local_tick): Try reading random seed from /dev/urandom
+
+2011-09-26   Andi Kleen <ak@linux.intel.com>
+
 	* hwint.h (HOST_WIDE_INT_PRINT_HEX_PURE): Add.
 	* lto-streamer.c (lto_get_section_name): Remove crc32_string.
  	Handle numerical random seed.

gcc/toplev.c

@@ -262,7 +262,17 @@ init_local_tick (void)
 {
   if (!flag_random_seed)
     {
-      /* Get some more or less random data.  */
+      /* Try urandom first. Time of day is too likely to collide. 
+	 In case of any error we just use the local tick. */
+
+      int fd = open ("/dev/urandom", O_RDONLY);
+      if (fd >= 0)
+        {
+          read (fd, &random_seed, sizeof (random_seed));
+          close (fd);
+        }
+
+      /* Now get the tick anyways  */
 #ifdef HAVE_GETTIMEOFDAY
       {
 	struct timeval tv;