Reapply "Expose starting_at_board_api to access_vectors"

This reverts commit d0c0e15cf16c812dd20e98da2a56e703cf149151.

Reason for revert: breakage fixed

Test: m selinux_policy
Change-Id: Ic3baccc83fd5369a62746910efe5be084a32883b
diff --git a/build/soong/policy.go b/build/soong/policy.go
index 5611ed0..4476f94 100644
--- a/build/soong/policy.go
+++ b/build/soong/policy.go
@@ -33,6 +33,7 @@
 
 // This order should be kept. checkpolicy syntax requires it.
 var policyConfOrder = []string{
+	"flagging_macros",
 	"security_classes",
 	"initial_sids",
 	"access_vectors",