[llvm] [llvm/DWARF] Recursively resolve DW_AT_signature references (PR #97423)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu` running on `sie-linux-worker3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/1857

Here is the relevant piece of the build log for the reference:
```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'cross-project-tests :: debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
Verifying -:	file format elf64-x86-64
Verifying .debug_abbrev...
Verifying .debug_info Unit Header Chain...
Verifying .debug_types Unit Header Chain...
Verifying non-dwo Units...
Verifying unit: 1 / 1, "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp"
Verifying dwo Units...
Verifying .debug_line...
Verifying .debug_str_offsets...
No errors.
Verifying -:	file format elf64-x86-64
Verifying .debug_abbrev...
Verifying .debug_info Unit Header Chain...
Verifying .debug_types Unit Header Chain...
Verifying non-dwo Units...
Verifying unit: 1 / 1, "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp"
Verifying dwo Units...
Verifying .debug_line...
Verifying .debug_str_offsets...
No errors.
Verifying -:	file format elf64-x86-64
Verifying .debug_abbrev...
Verifying .debug_info Unit Header Chain...
Verifying .debug_types Unit Header Chain...
Verifying non-dwo Units...
Verifying unit: 1 / 83, "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp"
error: Simplified template DW_AT_name could not be reconstituted:
         original: t3<int, false>
    reconstituted: t3

0x000000d6: DW_TAG_structure_type [20]   (0x0000000b)
              DW_AT_declaration [DW_FORM_flag_present]	(true)
              DW_AT_signature [DW_FORM_ref_sig8]	(0x384ddc13a7a92863)


0x0000000b: DW_TAG_compile_unit [52] *
              DW_AT_producer [DW_FORM_strp]	( .debug_str[0x00000000] = "clang version 19.0.0git (https://github.com/llvm/llvm-project.git e93df78bd46b585c0bdabdbdc95410e4c08b9d38)")
              DW_AT_language [DW_FORM_data2]	(DW_LANG_C_plus_plus_14)
              DW_AT_name [DW_FORM_strp]	( .debug_str[0x0000006c] = "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp")
              DW_AT_stmt_list [DW_FORM_sec_offset]	(0x00000000)
              DW_AT_comp_dir [DW_FORM_strp]	( .debug_str[0x0000010a] = "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/projects/cross-project-tests/debuginfo-tests/clang_llvm_roundtrip")
              DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000000)
              DW_AT_ranges [DW_FORM_sec_offset]	(0x00000000
                 [0x0000000000000000, 0x000000000000038d) ".text"
                 [0x0000000000000390, 0x00000000000003a6) ".text"
...

```

https://github.com/llvm/llvm-project/pull/97423