Make all the serialization code build for the Teensy too

Change-Id: Ib3442220581553d78bb30e42818203959d987d85
diff --git a/aos/util/BUILD b/aos/util/BUILD
index e712d54..af6faf5 100644
--- a/aos/util/BUILD
+++ b/aos/util/BUILD
@@ -1,10 +1,13 @@
 package(default_visibility = ["//visibility:public"])
 
+load("//tools:environments.bzl", "mcu_cpus")
+
 cc_library(
     name = "bitpacking",
     hdrs = [
         "bitpacking.h",
     ],
+    compatible_with = mcu_cpus,
     visibility = ["//visibility:public"],
     deps = [
         "//third_party/GSL",