Exception handling records are unlinked on function return. However, if
there is a musttail call before the return, that's the de-facto point of
termination and the unlinking instructions must be inserted *before*
that.

Fixes #119255

At the moment Windows 32 bit SEH state stores are only emitted for
throwing calls.

Windows 32 bit SEH state stores should also be emitted before SEH scope
begin and before SEH scope end.
An invalid inline memory access would otherwise not trigger unwinding,
in combination with /EHa.

This fixes #90946

This fixes issue #116583

When inalloca calls are inlined the static stack pointer saving prolog
of X86WinEHState breaks due to dynamic allocas.
In this case we need to update the saved esp for every inalloca and for
every stackrestore also related to inalloca.

It is simple to create the struct body up front, now that we have
transitioned to opaque pointers.

Convert almost every instance of:
  CreateCall(Intrinsic::getOrInsertDeclaration(...), ...)
to the equivalent CreateIntrinsic call.

Rename the function to reflect its correct behavior and to be consistent
with `Module::getOrInsertFunction`. This is also in preparation of
adding a new `Intrinsic::getDeclaration` that will have behavior similar
to `Module::getFunction` (i.e, just lookup, no creation).

Reverts the above commit, as it updates a common header function and
did not update all callsites:

  https://lab.llvm.org/buildbot/#/builders/29/builds/382

This reverts commit 6481dc57612671ebe77fe9c34214fba94e1b3b27.

Uses the new InsertPosition class (added in #94226) to simplify some of
the IRBuilder interface, and removes the need to pass a BasicBlock
alongside a BasicBlock::iterator, using the fact that we can now get the
parent basic block from the iterator even if it points to the sentinel.
This patch removes the BasicBlock argument from each constructor or call
to setInsertPoint.

This has no functional effect, but later on as we look to remove the
`Instruction *InsertBefore` argument from instruction-creation
(discussed
[here](https://discourse.llvm.org/t/psa-instruction-constructors-changing-to-iterator-only-insertion/77845)),
this will simplify the process by allowing us to deprecate the
InsertPosition constructor directly and catch all the cases where we use
instructions rather than iterators.

Work towards to the TODO item of removing method `Type::getPointerTo`
(as noted in llvm/include/llvm/IR/Type.h).