Flip on --bfbs-builtins

This makes it so that "builtin" flatbuffer attributes (e.g.,
force_align) get included in the generated reflection data.
Because I want to be able to support force_align in particular
in the static flatbuffers API, we need the force_align data
to get included in the generated schema information.

Change-Id: Ife408e214b139f53ad3ab34a07551747b08646f7
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/third_party/flatbuffers/build_defs.bzl b/third_party/flatbuffers/build_defs.bzl
index c1e568f..5f6d71b 100644
--- a/third_party/flatbuffers/build_defs.bzl
+++ b/third_party/flatbuffers/build_defs.bzl
@@ -21,6 +21,7 @@
     "--gen-object-api",
     "--gen-compare",
     "--keep-prefix",
+    "--bfbs-builtins",
     "--cpp-std",
     "c++17",
     "--require-explicit-ids",