Having a finite Depth (or recursion limit) for computeKnownBits is very
limiting, but is currently a load-bearing necessity, as all KnownBits
are recomputed on each call and there is no caching. As a prerequisite
for an effort to remove the recursion limit altogether, either using a
clever caching technique, or writing a easily-invalidable KnownBits
analysis, make the Depth argument in APIs in ValueTracking uniformly the
last argument with a default value. This would aid in removing the
argument when the time comes, as many callers that currently pass 0
explicitly are now updated to omit the argument altogether.

I'm looking for ways to simplify the Mem*Inst class structure, and these
two seem to have fairly minimal justification, so let's remove them.

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.

Detect cases where ABI attributes between the call-site and the called
function differ. For now this only handles argument attributes.

Inspired by
https://discourse.llvm.org/t/difference-between-call-site-attributes-and-declaration-attributes/83902.

Ensure store to const addrspace is not allowed by Linter.

Do not emit a warning if there are two null noalias arguments,
as they cannot be dereferenced anyway.

This is a common pattern for `@.omp_outlined`, which has some
optional noalias arguments.

We also need to check that the memory access LocationSize is not
scalable.

Don't assume the vector is fixed size. For scalable vectors, do
not report an error, as indices outside the minimum range may be
valid.