Generalize get_most_common_single_value to return n_th value & count

Generalize get_most_common_single_value to return n_th value & count

Currently get_most_common_single_value could only return the max hist
<value, count>, add sort after reading from disk, then it return nth value
in later use.  Rename it to get_nth_most_common_value.

gcc/ChangeLog:

2019-07-15  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	* ipa-profile.c (get_most_common_single_value): Use
	get_nth_most_common_value.
	* profile.c (sort_hist_value): New function.
	(compute_value_histograms): Call sort_hist_value to sort the
	values after loading from disk.
	* value-prof.c (get_most_common_single_value): Rename to ...
	get_nth_most_common_value.  Add input params n, return
	the n_th value and count.
	(gimple_divmod_fixed_value_transform): Use
	get_nth_most_common_value.
	(gimple_ic_transform): Likewise.
	(gimple_stringops_transform): Likewise.
	* value-prof.h (get_most_common_single_value): Add input params
	n, default to 0.

From-SVN: r273789