Add classlib and segments tool

This is the first step to track different segments of the classfile
backend in our benchmarks.

Change-Id: Ie16b8a3db76da54d54b2efc373a25cb9d10cb99b
diff --git a/.gitignore b/.gitignore
index 22b29da..de74144 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,6 +35,8 @@
 third_party/benchmarks/kotlin-benches.tar.gz
 third_party/benchmarks/santa-tracker
 third_party/benchmarks/santa-tracker.tar.gz
+third_party/classlib.tar.gz
+third_party/classlib
 third_party/chrome.tar.gz
 third_party/chrome
 third_party/dart-sdk