Reapply "[clang][DebugInfo] Emit DW_AT_object_pointer on function declarations with explicit `this`" (#123455)

This reverts commit c3a935e3f967f8f22f5db240d145459ee621c1e0.

The only change to the r

Reapply "[clang][DebugInfo] Emit DW_AT_object_pointer on function declarations with explicit `this`" (#123455)

This reverts commit c3a935e3f967f8f22f5db240d145459ee621c1e0.

The only change to the reverted commit is that this also updates
the OCaml bindings according to the C debug-info API changes.

The build failure originally introduced was:
```
FAILED: bindings/ocaml/debuginfo/debuginfo_ocaml.o /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bindings/ocaml/debuginfo/debuginfo_ocaml.o
cd /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bindings/ocaml/debuginfo && /usr/bin/ocamlfind ocamlc -c /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bindings/ocaml/debuginfo/debuginfo_ocaml.c -ccopt "-I/b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/bindings/ocaml/debuginfo/../llvm -D_GNU_SOURCE -D_DEBUG -D_GLIBCXX_ASSERTIONS -DEXPENSIVE_CHECKS -D_GLIBCXX_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/b/1/llvm-clang-x86_64-expensive-checks-debian/build/include -I/b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/include -DNDEBUG "
/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bindings/ocaml/debuginfo/debuginfo_ocaml.c: In function ‘llvm_dibuild_create_object_pointer_type’:
/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bindings/ocaml/debuginfo/debuginfo_ocaml.c:620:30: error: too few arguments to function ‘LLVMDIBuilderCreateObjectPointerType’
620 | LLVMMetadataRef Metadata = LLVMDIBuilderCreateObjectPointerType(
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bindings/ocaml/debuginfo/debuginfo_ocaml.c:23:
/b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/include/llvm-c/DebugInfo.h:880:17: note: declared here
880 | LLVMMetadataRef LLVMDIBuilderCreateObjectPointerType(LLVMDIBuilderRef Builder,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

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Revert "[clang][DebugInfo] Emit DW_AT_object_pointer on function declarations with explicit `this`" (#123455)

Reverts llvm/llvm-project#122928

[clang][DebugInfo] Emit DW_AT_object_pointer on function declarations with explicit `this` (#122928)

In https://github.com/llvm/llvm-project/pull/122897 we started attaching
`DW_AT_object_pointer`

[clang][DebugInfo] Emit DW_AT_object_pointer on function declarations with explicit `this` (#122928)

In https://github.com/llvm/llvm-project/pull/122897 we started attaching
`DW_AT_object_pointer` to function definitions. This patch does the same
but for function declarations (which we do for implicit object pointers
already).

Fixes https://github.com/llvm/llvm-project/issues/120974

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[clang][DebugInfo] Emit DW_AT_object_pointer on function definitions with explicit `this` (#122897)

We currently don't emit `DW_AT_object_pointer` on function declarations
or definitions. GCC suffe

[clang][DebugInfo] Emit DW_AT_object_pointer on function definitions with explicit `this` (#122897)

We currently don't emit `DW_AT_object_pointer` on function declarations
or definitions. GCC suffers from the same issue:
https://godbolt.org/z/h4jeT54G5

Fixing this will help LLDB in identifying static vs. non-static member
functions (see https://github.com/llvm/llvm-project/issues/120856).

If I interpreted the DWARFv5 spec correctly, it doesn't mandate this
attribute be present *only* for implicit object parameters:
```
If the member function entry describes a non-static member function,
then that entry has a DW_AT_object_pointer attribute whose value is a reference to
the formal parameter entry that corresponds to the object for which the
function is called.

That parameter also has a DW_AT_artificial attribute whose value is true.
```

This patch attaches the `DW_AT_object_pointer` for function
*defintions*. The declarations will be handled in a separate patch.

The part about `DW_AT_artificial` seems overly restrictive, and not true
for explicit object parameters. We probably should relax this part of
the DWARF spec.

Partially fixes https://github.com/llvm/llvm-project/issues/120974

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