[llvm] [PassBuilder][FatLTO] Expose FatLTO pipeline via pipeline string (PR #146048)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-debian` running on `gribozavr4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/21783

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: Other/fatlto.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -debug-pass-manager -passes='fatlto-pre-link<O2>' -disable-output /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Other/fatlto.ll 2>&1 | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Other/fatlto.ll # RUN: at line 1
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Other/fatlto.ll
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -debug-pass-manager '-passes=fatlto-pre-link<O2>' -disable-output /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Other/fatlto.ll
/b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Other/fatlto.ll:6:15: error: CHECK-NEXT: is not on the line after the previous match
; CHECK-NEXT: Running pass: FatLtoCleanup on [module]
              ^
<stdin>:39:1: note: 'next' match was here
Running pass: FatLtoCleanup on [module]
^
<stdin>:32:43: note: previous match ended here
Running pass: EmbedBitcodePass on [module]
                                          ^
<stdin>:33:1: note: non-matching line after previous match is here
Invalidating analysis: InnerAnalysisManagerProxy<llvm::FunctionAnalysisManager, llvm::Module> on [module]
^

Input file: <stdin>
Check file: /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Other/fatlto.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
        .
        .
        .
       34: Invalidating analysis: PreservedModuleHashAnalysis on [module] 
       35: Invalidating analysis: CallGraphAnalysis on [module] 
       36: Invalidating analysis: LazyCallGraphAnalysis on [module] 
       37: Invalidating analysis: InnerAnalysisManagerProxy<llvm::CGSCCAnalysisManager, llvm::Module> on [module] 
       38: Running analysis: InnerAnalysisManagerProxy<llvm::FunctionAnalysisManager, llvm::Module> on [module] 
       39: Running pass: FatLtoCleanup on [module] 
next:6     !~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  error: match on wrong line
       40: Running analysis: PreservedModuleHashAnalysis on [module] 
       41: Running pass: LowerTypeTestsPass on [module] 
       42: Running pass: EliminateAvailableExternallyPass on [module] 
       43: Running pass: ReversePostOrderFunctionAttrsPass on [module] 
       44: Running analysis: LazyCallGraphAnalysis on [module] 
        .
        .
        .
>>>>>>

--

...

```

</details>

https://github.com/llvm/llvm-project/pull/146048