Added missing system libraries and headers for bazel.

Change-Id: I966d28dd5a6677acc73c608a89efa30f8358b0dd
diff --git a/aos/linux_code/BUILD b/aos/linux_code/BUILD
index ce7b1b0..245acc6 100644
--- a/aos/linux_code/BUILD
+++ b/aos/linux_code/BUILD
@@ -22,6 +22,7 @@
   deps = [
     '//aos/common:once',
     '//aos/common:die',
+    '//external:libpthread',
   ],
 )