Correct timespec implementation [BZ #26232]

commit 04deeaa9
Author: Lucas A. M. Magalhaes <lamm@linux.ibm.com>
Date:   Fri Jul 10 19:41:06 2020 -0300

    Fix time/tst-cpuclock1 intermitent failures

has 2 issues:

1. It assumes time_t == long which is false on x32.
2. tst-timespec.c is compiled without -fexcess-precision=standard which
generates incorrect results on i686 in support_timespec_check_in_range:

  double ratio = (double)observed_norm / expected_norm;
  return (lower_bound <= ratio && ratio <= upper_bound);

This patch does

1. Compile tst-timespec.c with -fexcess-precision=standard.
2. Replace long with time_t.
3. Replace LONG_MIN and LONG_MAX with TYPE_MINIMUM (time_t) and
TYPE_MAXIMUM (time_t).