get_rnd_value() of ib_counter_t is unnecessarily complex

The sharded shared counter template ib_counter_t uses the function my_timer_cycles() as a source of pseudo-random numbers. On some platforms, my_timer_cycles() could return the constant value of 0. The function get_rnd_value() would work around this at run time (while it should have been done at compilation time) and invoke the function pthread_self() if the returned value happened to be 0.

To fix this, let us define a wrapper my_pseudo_random() that is either an alias of my_timer_cycles() or a wrapper for pthread_self(). In practice, the wrapper should only come into play on exotic operating systems or instruction set architectures.