commit-graph: rename commit_compare to oid_compare

The helper function commit_compare() actually compares object_id
structs, not commits. A future change to commit-graph.c will need
to sort commit structs, so rename this function in advance.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit-graph.c

@@ -770,7 +770,7 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
 	}
 }
 
-static int commit_compare(const void *_a, const void *_b)
+static int oid_compare(const void *_a, const void *_b)
 {
 	const struct object_id *a = (const struct object_id *)_a;
 	const struct object_id *b = (const struct object_id *)_b;
@@ -1039,7 +1039,7 @@ static uint32_t count_distinct_commits(struct write_commit_graph_context *ctx)
 			_("Counting distinct commits in commit graph"),
 			ctx->oids.nr);
 	display_progress(ctx->progress, 0); /* TODO: Measure QSORT() progress */
-	QSORT(ctx->oids.list, ctx->oids.nr, commit_compare);
+	QSORT(ctx->oids.list, ctx->oids.nr, oid_compare);
 
 	for (i = 1; i < ctx->oids.nr; i++) {
 		display_progress(ctx->progress, i + 1);