`getDebugNamesBucketAndHashCount` lures users to provide an array to
compute the bucket count using an O(n log n) sort. This is inefficient
as hash table based uniquifying is faster.
The performance issue matters less for Clang as the number of names is
relatively small. For `ld.lld --debug-names`, I plan to compute the
unique hash count as a side product of parallel entry pool computation,
and I just need a function to suggest a bucket count.
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