Let Clang emit `llvm.tbaa.errno` metadata in order to let LLVM
carry out optimizations around errno-writing libcalls to, as
long as it is proved the involved memory location does not alias
`errno`.

Previous discussion: https://discourse.llvm.org/t/rfc-modelling-errno-memory-effects/82972.

Tests exercizing TBAA metadata (both purposefully and not), and
previously generated via UTC, have been regenerated and updated
to version 6.

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended to be essentially NFC, replacing existing uses of `nocapture`
with `captures(none)` without adding any new analysis capabilities.
Making use of non-`none` values is left for a followup.

Some notes:
* `nocapture` will be upgraded to `captures(none)` by the bitcode
   reader.
* `nocapture` will also be upgraded by the textual IR reader. This is to
   make it easier to use old IR files and somewhat reduce the test churn in
   this PR.
* Helper APIs like `doesNotCapture()` will check for `captures(none)`.
* MLIR import will convert `captures(none)` into an `llvm.nocapture`
   attribute. The representation in the LLVM IR dialect should be updated
   separately.

If the gep is nusw (usually via inbounds) and the offset is
non-negative, we can infer nuw.

Proof: https://alive2.llvm.org/ce/z/ihztLy

reland https://github.com/llvm/llvm-project/pull/97373 after fixing
clang tests.

Confirmed with "ninja check-llvm" and "ninja check-clang"

In building AddrSpaceQualType
(https://github.com/llvm/llvm-project/pull/90048), there is a bug in
removeAddrSpaceQualType() for arrays. Arrays are weird because
qualifiers on the element type also count as qualifiers on the type, so
getSingleStepDesugaredType() can't remove the sugar on arrays. This
results in an infinite loop in removeAddrSpaceQualType. To fix the
issue, we use ASTContext::getUnqualifiedArrayType instead, which strips
the qualifier off the element type, then reconstruct the array type.