In `<__cxxabi_config.h>` there were a few things still around which
aren't ever actually used. This removes some of that cruft.

Implementation files using the Intel syntax typically explicitly specify
it. Do the same for the few files where applicable for AT&T.

This enables building LLVM with `-mllvm -x86-asm-syntax=intel` in one's
Clang config files (i.e. a global preference for Intel syntax).

Currently `OutputBuffer::GtIsGt` is used to tell us if we're inside
template arguments and have printed a '(' without a closing ')'. If so,
we don't need to quote '<' when printing it as part of a binary
expression inside a template argument. Otherwise we need to. E.g.,
```
foo<a<(b < c)>> // Quotes around binary expression needed.
```

LLDB's `TrackingOutputBuffer` has heuristics that rely on checking
whether we are inside template arguments, regardless of the current
parentheses depth. We've been using `isGtInsideTemplateArgs` for this,
but that isn't correct. Resulting in us incorrectly tracking the
basename of function like:
```
void func<(foo::Enum)1>()
```
Here `GtIsGt > 0` despite us being inside template arguments (because we
incremented it when seeing '(').

This patch adds a `isInsideTemplateArgs` API which LLDB will use to more
accurately track parts of the demangled name.

To make sure this API doesn't go untested in the actual libcxxabi
test-suite, I changed the existing `GtIsGt` logic to use it. Also
renamed the various variables/APIs involved to make it (in my opinion)
more straightforward to understand what's going on. But happy to rename
it back if people disagree.

Also adjusted LLDB to use the newly introduced API (and added a
unit-test that would previously fail).

In https://github.com/llvm/llvm-project/pull/137947 I refactored the
script and added a `copy_files` function, which takes the header files
to copy as an argument.

But because the list of headers is a space separated string, we need to
quote the string. Otherwise we would just copy the first header in the
list.

This patch also adds an `echo` statement in the `copy_files` loop to
print the source/destination. Confirming that the files are copied as
expected.
```
$ libcxxabi/src/demangle/cp-to-llvm.sh
This will overwrite the copies of ItaniumDemangle.h ItaniumNodes.def StringViewExtras.h Utility.h in ../../../llvm/include/llvm/Demangle and DemangleTestCases.inc in ../../../llvm/include/llvm/Demangle/../Testing/Demangle; are you sure? [y/N]y
Copying ./ItaniumDemangle.h to ../../../llvm/include/llvm/Demangle/ItaniumDemangle.h
Copying ./ItaniumNodes.def to ../../../llvm/include/llvm/Demangle/ItaniumNodes.def
Copying ./StringViewExtras.h to ../../../llvm/include/llvm/Demangle/StringViewExtras.h
Copying ./Utility.h to ../../../llvm/include/llvm/Demangle/Utility.h
Copying ../../test/DemangleTestCases.inc to ../../../llvm/include/llvm/Demangle/../Testing/Demangle/DemangleTestCases.inc
```

Luckily there weren't any out-of-sync changes introduced in the
meantime.

4eed68357e4361b3a3aeb349dec2612cfb74c8cc updated the LLVM side but did
not bump the libc++abi version. Bump the libc++abi version to fix the
test failure caused by the versions differing.

An LLVM 19-aligned libc++ was released with macOS 15.4 (and corresponding OSes),
and LLVM-20 aligned with macOS 26.0. This patch adds availability markup to
reflect that.

This patch reverts e15025dd and 88e15b781 which were temporary measures
until we had figured out the underlying issues. It turns out that recent
OSes updated localization data, removing the need for several Apple-specific
workarounds in the tests.

Fixes #135385

This hardens the unwinding logic and datastructures on systems
that support pointer authentication.

The approach taken to hardening is to harden the schemas of as many
high value fields in the myriad structs as possible, and then also
explicitly qualify local variables referencing privileged or security
critical values.

This does introduce ABI linkage between libcxx, libcxxabi, and
libunwind but those are in principle separate from the OS itself
so we've kept the schema definitions in the library specific headers
rather than ptrauth.h

Based on review feedback in #160026.

This makes the substitution a lot more clear now that there is no
documentation around %T.

---------

Co-authored-by: Louis Dionne <ldionne.2@gmail.com>