We will only regsiter top level types and decls in ASTWriter and
we will register the sub types and decls during the process of writing
types and decls. So that the ID for the types in the sub level can be
different if the writing decl process changes the order of the to-be-
emitted type queues. This is not ideal since it causes unnecessary
changes especially in no transitive changes model.
This patch migrates the issue by regsitering special types before
regsitering decls. This make sure that the special types in the 2nd
top level can be registered early than the decls. But it might still be
problematic if there are more levels in the special types. Luckily we
just don't have such special types.
I found we may insert unused implciit declarations like AArch SVE
declarations by default on AArch64 due to we will insert that by
default. But it should be completely redundant and this patch tries to
remove that.
