ftrace_reader: Move some code for generating the protos into tools/

We put too much code into src/ when refactoring the ftrace format
reader code. This puts some of the stuff we don't really need back
under tools/.

Bug: 71844955
Change-Id: I75cd18c7faedcab7806e83f93238b282341a0a68
diff --git a/BUILD.gn b/BUILD.gn
index 2787f6e..7cc1af7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -52,6 +52,7 @@
     "src/ipc:perfetto_ipc_unittests",
     "src/protozero:protozero_unittests",
     "src/tracing:tracing_unittests",
+    "tools/ftrace_proto_gen:ftrace_proto_gen_unittests",
   ]
   if (!build_with_chromium) {
     deps += [ "tools/sanitizers_unittests" ]