As we are now Sema-complete for OpenACC 3.4 (and thus have a conforming
implementation, in all modes), we can now set the _OPENACC macro
correctly.

Additionally, we remove the temporary 'override' functionality, which
was intended to allow people to experiment with this. We aren't having a
deprecation period as OpenACC support is still considered experimental.

This PR removes the command line parsing workaround introduced in
https://github.com/llvm/llvm-project/pull/146342 by moving
`LangOptions::ExceptionHandling` to `CodeGenOptions` that get parsed
even for IR input. Additionally, this improves layering, where the
codegen library now checks `CodeGenOptions` instead of `LangOptions` for
exception handling. (This got enabled by
https://github.com/llvm/llvm-project/pull/146422.)

Some `LangOptions` duplicate their `CodeGenOptions` counterparts. My
understanding is that this was done solely because some infrastructure
(like preprocessor initialization, serialization, module compatibility
checks, etc.) were only possible/convenient for `LangOptions`. This PR
implements the missing support for `CodeGenOptions`, which makes it
possible to remove some duplicate `LangOptions` fields and simplify the
logic. Motivated by https://github.com/llvm/llvm-project/pull/146342.

Alas reflection pushed p2719 out of C++26, so this PR changes the
diagnostics to reflect that for now type aware allocation is
functionally a clang extension.

When passing `-save-temps` to clang, the generated preprocessed output
uses gnu line markers. This unexpectedly triggers gnu-line-marker
warnings when used with `-Weverything` or `-pedantic`. Even worse,
compilation fails if `-Werror` is used.

This change suppresses gnu-line-marker warnings when invoking clang with
input from a preprocessor job and the user has not otherwise explictly
specified `-Wgnu-line-marker` somewhere on the command line. Note that
this does apply to user provided preprocessed files.

fixes #63802

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.

The allocation interposition mode had a number of issues, which are
primarily addressed in the library component via
<https://github.com/ROCm/rocThrust/pull/543>. However, it is necessary
to interpose some additional symbols, which this patch does.
Furthermore, to implement this in a compatible way, we guard the new
implementation under a V1 macro, which is defined in addition to the
existing `__HIPSTDPAR_INTERPOSE_ALLOC__` one.

This adds

- The parsing of `trivially_relocatable_if_eligible`,
`replaceable_if_eligible` keywords
- `__builtin_trivially_relocate`, implemented in terms of memmove. In
the future this should
- Add the appropriate start/end lifetime markers that llvm does not have
(`start_lifetime_as`)
     - Add support for ptrauth when that's upstreamed

- the `__builtin_is_cpp_trivially_relocatable` and
`__builtin_is_replaceable` traits


Fixes #127609