Fix spurious output in configure

If sizeof off_t is 4, then configure will print a line saying just "0"
after the test.  This is the output of the following "expr" command.
If we are using expr just for the exit code, the output should be sent
to /dev/null, as is done elsewhere.

configure

@@ -15387,7 +15387,7 @@ _ACEOF
 
 # If we don't have largefile support, can't handle segment size >= 2GB.
 if test "$ac_cv_sizeof_off_t" -lt 8; then
-  if expr $RELSEG_SIZE '*' $blocksize '>=' 2 '*' 1024 '*' 1024; then
+  if expr $RELSEG_SIZE '*' $blocksize '>=' 2 '*' 1024 '*' 1024 >/dev/null; then
     as_fn_error $? "Large file support is not enabled. Segment size cannot be larger than 1GB." "$LINENO" 5
   fi
 fi

configure.ac

@@ -1753,7 +1753,7 @@ AC_CHECK_SIZEOF([off_t])
 
 # If we don't have largefile support, can't handle segment size >= 2GB.
 if test "$ac_cv_sizeof_off_t" -lt 8; then
-  if expr $RELSEG_SIZE '*' $blocksize '>=' 2 '*' 1024 '*' 1024; then
+  if expr $RELSEG_SIZE '*' $blocksize '>=' 2 '*' 1024 '*' 1024 >/dev/null; then
     AC_MSG_ERROR([Large file support is not enabled. Segment size cannot be larger than 1GB.])
   fi
 fi