Add a new `CreateIntrinsic` overload with no `Types`, useful for
creating calls to non-overloaded intrinsics that don't need additional
mangling.

Identified with misc-include-cleaner.

Convert many instances of:
  Fn = Intrinsic::getOrInsertDeclaration(...);
  CreateCall(Fn, ...)
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).

Use const SCEV * explicitly in more places to prepare for
https://github.com/llvm/llvm-project/pull/91961. Split off as suggested.

This is a helper to avoid writing `getModule()->getDataLayout()`. I
regularly try to use this method only to remember it doesn't exist...

`getModule()->getDataLayout()` is also a common (the most common?)
reason why code has to include the Module.h header.

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.

This patch adds a two-argument SetInsertPoint method to IRBuilder that
takes a block/iterator instead of an instruction, and updates many call
sites to use it. The motivating reason for doing this is given here [0],
we'd like to pass around more information about the position of debug-info
in the iterator object. That necessitates passing iterators around most of
the time.

[0] https://discourse.llvm.org/t/rfc-instruction-api-changes-needed-to-eliminate-debug-intrinsics-from-ir/68939

Differential Revision: https://reviews.llvm.org/D152468

The corresponding function definition was removed by:

  commit af45907653fd312264632b616eff0fad1ae1eb2e
  Author: Sjoerd Meijer <sjoerd.meijer@arm.com>
  Date:   Mon Jun 29 15:40:03 2020 +0100