For swift async code, we need to use a debug intrinsic that behaves like
an llvm.dbg.declare but can take any location type rather than just a
pointer or integer.

To solve this, a new debug instrinsic called llvm.dbg.declare_value has
been created, which behaves exactly like an llvm.dbg.declare but can
take non pointer and integer location types.

More information here:
https://discourse.llvm.org/t/rfc-introduce-new-llvm-dbg-coroframe-entry-intrinsic/88269

This is the first patch as part of a stack of patches, with the one
succeeding it being: https://github.com/llvm/llvm-project/pull/168134

Per https://llvm.org/docs/CodingStandards.html#include-as-little-as-possible this improves compilation time, while not being too intrusive on the codebase.

These checks ensure that retained nodes of a DISubprogram belong to the
subprogram.

Tests with incorrect IR are fixed. We should not have variables of one subprogram present in retained nodes of other subprograms.

Also, interface for accessing DISubprogram's retained nodes is slightly
refactored. `DISubprogram::visitRetainedNodes` and
`DISubprogram::forEachRetainedNode` are added to avoid repeating checks
like
```
if (const auto *LV = dyn_cast<DILocalVariable>(N))
  ...
else if (const auto *L = dyn_cast<DILabel>(N))
  ...
else if (const auto *IE = dyn_cast<DIImportedEntity>(N))
  ...
```

This fixes a few typos noticed while browsing around IR-related files.

Add create file with checksum to the C interface

This patch sets up `DICompileUnit` to support the DWARFv6
`DW_AT_language_name` and `DW_AT_language_version` attributes (which are
set to replace `DW_AT_language`). This patch changes the
`DICompileUnit::SourceLanguage` field type to a `DISourceLanguageName`
that encapsulates the notion of "versioned vs. unversioned name". A
"versioned" name is one that has an associated version stored separately
in `DISourceLanguageName::Version`.

This patch just changes all the clients of the `getSourceLanguage` API
to the expect a `DISourceLanguageName`. Currently they all just `assert`
(via `DISourceLanguageName::getUnversionedName`) that we're dealing with
"unversioned names" (i.e., the pre-DWARFv6 language codes). In follow-up
patches (e.g., draft is at
https://github.com/llvm/llvm-project/pull/162261), when we start
emitting versioned language codes, the `getUnversionedName` calls can
then be adjusted to `getName`.

**Implementation considerations**

* We could have added a new member to `DICompileUnit` alongside the
existing `SourceLanguage` field. I don't think this would have made the
transition any simpler (clients would still need to be aware of
"versioned" vs. "unversioned" language names). I felt that encapsulating
this inside a `DISourceLanguageName` was easier to reason about for
maintainers.
* Currently DISourceLanguageName is a `12` byte structure. We could
probably pack all the info inside a `uint64_t` (16-bits for the name,
32-bits for the version, 1-bit for answering the `hasVersionedName`).
Just to keep the prototype simple I used a `std::optional`. But since
the guts of the structure are hidden, we can always change the layout to
a more compact representation instead.

**How to review**

* The new `DISourceLanguageName` structure is defined in
`DebugInfoMetadata.h`. All the other changes fall out from changing the
`DICompileUnit::SourceLanguage` from `unsigned` to
`DISourceLanguageName`.

Inliner/IROutliner/CodeExtractor all uses the
updateLoopMetadataDebugLocations helper in order to modify debug
location related to loop metadata. However, the helper has only
been updating DILocation nodes found as operands to the first level
of the MD_loop metadata. There could however be more DILocations
as part of the various kinds of followup metadata. A typical example
would be llvm.loop metadata like this

  !6 = distinct !{!6, !7, !8, !9, !10, !11}
  !7 = !DILocation(line: 6, column: 3, scope: !3)
  !8 = !DILocation(line: 7, column: 22, scope: !3)
  !11 = !{!"llvm.loop.distribute.followup_all", !7, !8, ..., !14}
  !14 = !{!"llvm.loop.vectorize.followup_all", !7, !8, ...}

Instead of just updating !7 and !8 in !6, this patch make sure that
we now recursively update the DILocations in !11 and !14 as well.

Fixes #141568

In order to better see what's going on during ThinLTO linking, this PR
adds more profile tags when using `--time-trace` on a `lld-link.exe`
invocation.

After PR, linking `clang.exe`:

<img width="3839" height="2026" alt="Capture d’écran 2025-09-02 082021"
src="https://github.com/user-attachments/assets/bf0c85ba-2f85-4bbf-a5c1-800039b56910"
/>

Linking a custom (Unreal Engine game) binary gives a completly
different picture, probably because of using Unity files, and the sheer
amount of input files (here, providing over 60 GB of .OBJs/.LIBs).

<img width="1940" height="1008" alt="Capture d’écran 2025-09-02 102048"
src="https://github.com/user-attachments/assets/60b28630-7995-45ce-9e8c-13f3cb5312e0"
/>

Correct few typos: 'seperate' -> 'separate' .