randread: don't require -lrt

Programs like 'sort' were linking to -lrt in order to get
clock_gettime, but this was misguided: it wasted considerable
resources while gaining at most 10 bits of entropy.  Almost nobody
needs the entropy, and there are better ways to get much better
entropy for people who do need it.
* gl/lib/rand-isaac.c (isaac_seed): Include <sys/time.h> not
"gethrxtime.h".
(isaac_seed): Use gettimeofday rather than gethrxtime.
* gl/modules/randread (Depends-on): Depend on gettimeofday
and not gethrxtime.
* src/Makefile.am (mktemp_LDADD, shred_LDADD, shuf_LDADD, sort_LDADD):
(tac_LDADD): Omit $(LIB_GETHRXTIME); no longer needed.

gl/lib/rand-isaac.c

@@ -35,10 +35,9 @@
 #include "rand-isaac.h"
 
 #include <string.h>
+#include <sys/time.h>
 #include <unistd.h>
 
-#include "gethrxtime.h"
-
 
 /* This index operation is more efficient on many processors */
 #define ind(mm, x) \
@@ -292,7 +291,8 @@ isaac_seed (struct isaac_state *s)
   { gid_t t = getgid ();   ISAAC_SEED (s, t); }
 
   {
-    xtime_t t = gethrxtime ();
+    struct timeval t;
+    gettimeofday (&t, NULL);
     ISAAC_SEED (s, t);
   }
 

gl/modules/randread

@@ -11,7 +11,7 @@ Depends-on:
 error
 exitfail
 fopen-safer
-gethrxtime
+gettimeofday
 quotearg
 stdbool
 stdint

src/Makefile.am

@@ -328,13 +328,8 @@ ls_LDADD += $(LIB_CLOCK_GETTIME)
 pr_LDADD += $(LIB_CLOCK_GETTIME)
 touch_LDADD += $(LIB_CLOCK_GETTIME)
 
-# for gethrxtime, randint, randread, gen_tempname, mkstemp
+# for gethrxtime
 dd_LDADD += $(LIB_GETHRXTIME)
-mktemp_LDADD += $(LIB_GETHRXTIME)
-shred_LDADD += $(LIB_GETHRXTIME)
-shuf_LDADD += $(LIB_GETHRXTIME)
-sort_LDADD += $(LIB_GETHRXTIME)
-tac_LDADD += $(LIB_GETHRXTIME)
 
 # for cap_get_file
 ls_LDADD += $(LIB_CAP)