sstable: populate CompareSuffixes on test4bSuffixComparer

Previously, the test4bSuffixComparer test comparer wasn't setting
CompareSuffixes. Update the comparer to simply copy the default comparer
override Split and Name.

sstable/suffix_rewriter_test.go

@@ -240,3 +240,16 @@ func BenchmarkRewriteSST(b *testing.B) {
 		})
 	}
 }
+
+var test4bSuffixComparer = func() *base.Comparer {
+	c := new(base.Comparer)
+	*c = *base.DefaultComparer
+	c.Split = func(key []byte) int {
+		if len(key) > 4 {
+			return len(key) - 4
+		}
+		return len(key)
+	}
+	c.Name = "comparer-split-4b-suffix"
+	return c
+}()

sstable/writer_test.go

@@ -1200,17 +1200,3 @@ func runWriterBench(b *testing.B, keys [][]byte, comparer *base.Comparer, format
 		})
 	}
 }
-
-var test4bSuffixComparer = &base.Comparer{
-	Compare:   base.DefaultComparer.Compare,
-	Equal:     base.DefaultComparer.Equal,
-	Separator: base.DefaultComparer.Separator,
-	Successor: base.DefaultComparer.Successor,
-	Split: func(key []byte) int {
-		if len(key) > 4 {
-			return len(key) - 4
-		}
-		return len(key)
-	},
-	Name: "comparer-split-4b-suffix",
-}