This annotates the `Twine` passed to the constructors of the various
DiagnosticInfo subclasses with `[[clang::lifetimebound]]`, which causes
us to warn when we would try to print the twine after it had already
been destructed.

We also update `DiagnosticInfoUnsupported` to hold a `const Twine &`
like all of the other DiagnosticInfo classes, since this warning allows
us to clean up all of the places where it was being used incorrectly.

These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

We can use *Set::insert_range to collapse:

  for (auto Elem : Range)
    Set.insert(E);

down to:

  Set.insert_range(Range);

In some cases, we can further fold that into the set declaration.

This avoids doing a Triple -> std::string -> Triple round trip in lots
of places, now that the Module stores a Triple.

The module currently stores the target triple as a string. This means
that any code that wants to actually use the triple first has to
instantiate a Triple, which is somewhat expensive. The change in #121652
caused a moderate compile-time regression due to this. While it would be
easy enough to work around, I think that architecturally, it makes more
sense to store the parsed Triple in the module, so that it can always be
directly queried.

For this change, I've opted not to add any magic conversions between
std::string and Triple for backwards-compatibilty purses, and instead
write out needed Triple()s or str()s explicitly. This is because I think
a decent number of them should be changed to work on Triple as well, to
avoid unnecessary conversions back and forth.

The only interesting part in this patch is that the default triple is
Triple("") instead of Triple() to preserve existing behavior. The former
defaults to using the ELF object format instead of unknown object
format. We should fix that as well.

#125983

\#92331 tried to make `ObjCARCContractPass` by default, but it caused a
regression on O0 builds and was reverted.
This patch trys to bring that back by:

1. reverts the
[revert](https://github.com/llvm/llvm-project/commit/1579e9ca9ce17364963861517fecf13b00fe4d8a).
2. `createObjCARCContractPass` only on optimized builds.

Tests are updated to refelect the changes. Specifically, all `O0` tests
should not include `ObjCARCContractPass`

Signed-off-by: Peter Rong <PeterRong@meta.com>

LTOBackend inlined it a while ago and now uses a static copy. This API
was unused.

We can always restore it at some point if it's needed, but right now
it's just bloat.

This reverts commit 8cc8e5d6c6ac9bfc888f3449f7e424678deae8c2.
This reverts commit dae55c89835347a353619f506ee5c8f8a2c136a7.

Causes major compile-time regressions for unoptimized builds.