compiler: export indexed type data, read unexported types lazily
Introduce a new "types" command to the export data to record the
number of types and the size of their export data. It is immediately
followed by new "type" commands that can be indexed. Parse all the
exported types immediately so that we register them, but parse other
type data only as needed.
Reviewed-on: https://go-review.googlesource.com/c/143022
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@265409 138bc75d-0d04-0410-961f-82ee72b054a4