DWARF calculate the number of indexed addresses.

DWARF calculate the number of indexed addresses.

The length in the .debug_addr unit header was calculated using the number
of elements in the addr_index_table. This is wrong because the entries in
the table are refcounted and only those with a refcount > 0 are actually
put in the index. Add a helper function count_index_addrs to get the
correct number of addresses in the index.

gcc/ChangeLog:

	* dwarf2out.c (count_index_addrs): New function.
	(dwarf2out_finish): Use count_index_addrs to calculate addrs_length.

From-SVN: r260251