Opaque ptr cleanup effort (NFC).

This reverts commit cb5f239363a3c94db5425c105fcd45e77d2a16a9.

This reverts commit ed3e3ee9e30dfbffd2170a770a49b36a7f444916.

This patch adds several missing GlobalList modifier functions, like
removeGlobalVariable(), eraseGlobalVariable() and insertGlobalVariable().
There is no longer need to access the list directly so it also makes
getGlobalList() private.

Differential Revision: https://reviews.llvm.org/D144027

Adjust `optimizeGlobalCtorsList` to handle the case of different priorities.
This addresses the issue https://github.com/llvm/llvm-project/issues/55083.

Test plan: ninja check-all

Differential revision: https://reviews.llvm.org/D125278

Previously all entries in global_ctors had to have the void()* type and
we'd skip evaluating bitcasted functions. With opaque pointers we may
see the function directly.

Fixes #55147.

Reviewed By: #opaque-pointers, nikic

Differential Revision: https://reviews.llvm.org/D124553

If there are no ctors, then this can have an arbirary zero-sized
value. The current code checks for null, but it could also be
undef or poison.

Replacing the specific null check with a check for
non-ConstantArray.

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636