Linux glibc has deprecated ftime resutlting in a compile error on Fedora-32.

Per manual clock_gettime is the suggested replacement. Because my_timer_milliseconds
is a relative time used by largely the perfomrance schema, CLOCK_MONOTONIC_COARSE
is used. This has been available since Linux-2.6.32.

The low overhead is shows in the unittest:

    $ unittest/mysys/my_rdtsc-t
    1..11
    # ----- Routine ---------------
    # myt.cycles.routine          :             5
    # myt.nanoseconds.routine     :            11
    # myt.microseconds.routine    :            13
    # myt.milliseconds.routine    :            18
    # myt.ticks.routine           :            17
    # ----- Frequency -------------
    # myt.cycles.frequency        :    3596597014
    # myt.nanoseconds.frequency   :    1000000000
    # myt.microseconds.frequency  :       1000000
    # myt.milliseconds.frequency  :          1039
    # myt.ticks.frequency         :           103
    # ----- Resolution ------------
    # myt.cycles.resolution       :             1
    # myt.nanoseconds.resolution  :             1
    # myt.microseconds.resolution :             1
    # myt.milliseconds.resolution :             1
    # myt.ticks.resolution        :             1
    # ----- Overhead --------------
    # myt.cycles.overhead         :           118
    # myt.nanoseconds.overhead    :           234
    # myt.microseconds.overhead   :           222
    # myt.milliseconds.overhead   :            30
    # myt.ticks.overhead          :          4946
    ok 1 - my_timer_init() did not crash
    ok 2 - The cycle timer is strictly increasing
    ok 3 - The cycle timer is implemented
    ok 4 - The nanosecond timer is increasing
    ok 5 - The nanosecond timer is implemented
    ok 6 - The microsecond timer is increasing
    ok 7 - The microsecond timer is implemented
    ok 8 - The millisecond timer is increasing
    ok 9 - The millisecond timer is implemented
    ok 10 - The tick timer is increasing
    ok 11 - The tick timer is implemented