[llvm] [Utils] Consolidate `LockstepReverseIterator` into own header (NFC) (PR #116657)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-x86_64-debian-fast` running on `gribozavr4` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/56/builds/19156

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
In file included from /b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h:23:
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/CodeGen/BasicTTIImpl.h:2894:14: warning: parameter 'CondTy' not found in the function declaration [-Wdocumentation]
  /// \param CondTy Conditional type for the Select instruction.
             ^~~~~~
In file included from /b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp:42:
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/MC/TargetRegistry.h:85:12: warning: parameter 'ShowInst' not found in the function declaration [-Wdocumentation]
/// \param ShowInst - Whether to show the MCInst representation inline with
           ^~~~~~~~
16 warnings generated.
12.881 [1074/54/5026] Building CXX object lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o
FAILED: lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes /usr/bin/ccache /usr/bin/clang++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/b/1/clang-x86_64-debian-fast/llvm.obj/lib/Transforms/Utils -I/b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils -I/b/1/clang-x86_64-debian-fast/llvm.obj/include -I/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include -std=c++11 -Wdocumentation -Wno-documentation-deprecated-sync -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -MD -MT lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o -MF lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o.d -o lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o -c /b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
In file included from /b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:33:
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/Analysis/MemorySSAUpdater.h:269:14: warning: parameter 'MPhiMap,' not found in the function declaration [-Wdocumentation]
  /// \param MPhiMap, is created in the caller of this private method, and maps
             ^~~~~~~~
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/Analysis/MemorySSAUpdater.h:269:14: note: did you mean 'MPhiMap'?
  /// \param MPhiMap, is created in the caller of this private method, and maps
             ^~~~~~~~
             MPhiMap
In file included from /b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:54:
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/IR/MDBuilder.h:64:14: warning: parameter 'Do' not found in the function declaration [-Wdocumentation]
  /// @param Do these weights come from __builtin_expect*
             ^~
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/IR/MDBuilder.h:64:14: note: did you mean 'IsExpected'?
  /// @param Do these weights come from __builtin_expect*
             ^~
             IsExpected
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/IR/MDBuilder.h:78:14: warning: parameter 'Do' not found in the function declaration [-Wdocumentation]
  /// @param Do these weights come from __builtin_expect*
             ^~
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/IR/MDBuilder.h:78:14: note: did you mean 'IsExpected'?
  /// @param Do these weights come from __builtin_expect*
             ^~
             IsExpected
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2503:3: error: reference to 'LockstepReverseIterator' is ambiguous
  LockstepReverseIterator<true> LRI(UnconditionalPreds);
  ^
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/Transforms/Utils/LockstepReverseIterator.h:41:7: note: candidate found by name lookup is 'llvm::LockstepReverseIterator'
class LockstepReverseIterator
      ^
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1787:7: note: candidate found by name lookup is '(anonymous namespace)::LockstepReverseIterator'
class LockstepReverseIterator {
      ^
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2533:44: error: reference to 'LockstepReverseIterator' is ambiguous
    auto ProfitableToSinkInstruction = [&](LockstepReverseIterator<true> &LRI) {
                                           ^
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/include/llvm/Transforms/Utils/LockstepReverseIterator.h:41:7: note: candidate found by name lookup is 'llvm::LockstepReverseIterator'
class LockstepReverseIterator

```

</details>

https://github.com/llvm/llvm-project/pull/116657