[lld] [llvm] [DTLTO][LLD][ELF] Support bitcode members of thin archives (PR #149425)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `cross-project-tests,lld` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/21043

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'lld :: ELF/dtlto/archive-thin.test' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 5
rm -rf Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp && split-file Z:\b\llvm-clang-x86_64-sie-win\llvm-project\lld\test\ELF\dtlto\archive-thin.test Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp && cd Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp
# executed command: rm -rf 'Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp'
# note: command had no output on stdout or stderr
# executed command: split-file 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\lld\test\ELF\dtlto\archive-thin.test' 'Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp'
# note: command had no output on stdout or stderr
# executed command: cd 'Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp'
# note: command had no output on stdout or stderr
# RUN: at line 7
sed 's/@t1/@t2/g' t1.ll > t2.ll
# executed command: sed s/@t1/@t2/g t1.ll
# note: command had no output on stdout or stderr
# RUN: at line 8
sed 's/@t1/@t3/g' t1.ll > t3.ll
# executed command: sed s/@t1/@t3/g t1.ll
# note: command had no output on stdout or stderr
# RUN: at line 10
z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe -thinlto-bc t1.ll -o t1.bc
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe' -thinlto-bc t1.ll -o t1.bc
# note: command had no output on stdout or stderr
# RUN: at line 11
z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe -thinlto-bc t2.ll -o t2.bc
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe' -thinlto-bc t2.ll -o t2.bc
# note: command had no output on stdout or stderr
# RUN: at line 12
z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe -thinlto-bc t3.ll -o t3.bc
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe' -thinlto-bc t3.ll -o t3.bc
# note: command had no output on stdout or stderr
# RUN: at line 14
llvm-ar rcs t1.a t1.bc --thin
# executed command: llvm-ar rcs t1.a t1.bc --thin
# note: command had no output on stdout or stderr
# RUN: at line 18
mkdir lib
# executed command: mkdir lib
# note: command had no output on stdout or stderr
# RUN: at line 19
llvm-ar rcs lib/t2.a t2.bc --thin
# executed command: llvm-ar rcs lib/t2.a t2.bc --thin
# note: command had no output on stdout or stderr
# RUN: at line 21
llvm-ar rcs t3.a Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp/lib/../t3.bc --thin
# executed command: llvm-ar rcs t3.a 'Z:\b\llvm-clang-x86_64-sie-win\build\tools\lld\test\ELF\dtlto\Output\archive-thin.test.tmp/lib/../t3.bc' --thin
# note: command had no output on stdout or stderr
# RUN: at line 25
...

```

</details>

https://github.com/llvm/llvm-project/pull/149425