[Bug ada/65524] gnatbind generates decrementing the unexisting elab-counter into finalize_library

["demoonlit at panathenaia dot halfmoon.jp" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65524

--- Comment #2 from yuta tomino <demoonlit at panathenaia dot halfmoon.jp> ---
Created attachment 35115
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35115&action=edit
example

I found the way of reproducing.

A tiny change of a-tags.ads is necessary.
Insert "is null" into Ada.Tags.Register_Tag to suppress the elaboration.
(Is there a pragma or restriction for this purpose?)

Note, Unregister_Tag is unrelated.

And, make a package as Pure or Preelaborate. Add a tagged type.
So the package would have _finalize_spec without _elabs.

(The direct cause of this case is the asymmetry that _elabs is not generated if
Register_Tag is null, against that,
_fialize_spec is always generated even if Unregister_Tag is null.
Register/Unregister_XXX are sometimes suppressed in parts of customized
runtimes.
My customized runtime satisfies the conditions about this time.
However, the way is only example for reproducing.
I think another approach is possibility because Build_Finalizer in exp_ch7.adb
is very complex...)

And then, prepare a main subprogram using the package. Compile and gnatbind.
See b~main.adb.

The log of compiling the attached example:

 % gnatmake -a -gnatp -g main
 gnatbind -x main.ali
 gnatlink main.ali -g
 b~main.adb:31:10: "E81" is undefined (more references follow)
 b~main.adb:34:07: "E05" is undefined (more references follow)
 gnatmake: *** link failed.

By the way, sorry, I realized that my first patch is not proper fix.
For multiple-elaboration, an elaboration-counter should be generated and
incremented in adainit when a _finalize_spec/body is existing, even if _elabs
is not existing.

Thanks.