Upgrade benchmark library to v1.7.1 release.
diff --git a/third_party/benchmark b/third_party/benchmark
index bf585a2..d572f47 160000
--- a/third_party/benchmark
+++ b/third_party/benchmark
@@ -1 +1 @@
-Subproject commit bf585a2789e30585b4e3ce6baf11ef2750b54677
+Subproject commit d572f4777349d43653b21d6c2fc63020ab326db2