Bug 27466

In partition_dups_1, we use heuristics to decide whether to convert a partition into a partial unit.
 
These heuristics use the number of unique referrer CUs, registered in the cnt variable.

This cnt is used to compute both:
- the current size of the partition:
  "orig_size = size * cnt;" 
- to size of imports of partial unit to be created:
  "+ (part_lang != 0 ? 0 : import_size * cnt)".

With odr, the duplicate chain is no longer isomorph, and consequently orig_size cannot any longer be calculated using size * cnt.

Then, the number of unique referrer CUs is the correct number to use for the number of imports.  But due to recent commit "Fix DW_AT_decl_file for odr
", the cnt variable may be lower than the actual number of unique referrer CUs.