tools: add build tag on tools.go to fix IJ error

Change-Id: I26eef5fb4275a240be06c829a193fd41694d7465

tools/tools.go

@@ -1,3 +1,5 @@
+// +build tools
+
 // package tool pins a number of Go dependencies that we use. Go builds really fast,
 // so wherever we can, we just build from source rather than pulling in third party binaries.
 package main