[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 `bolt-x86_64-ubuntu-nfc` running on `bolt-worker` while building `llvm` at step 7 "build-bolt".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/92/builds/14046

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

```
Step 7 (build-bolt) failure: build (failure)
...
11.565 [171/15/202] Building CXX object tools/bolt/lib/Target/X86/CMakeFiles/LLVMBOLTTargetX86.dir/X86MCPlusBuilder.cpp.o
In file included from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/bolt/include/bolt/Core/BinarySection.h:18,
                 from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/bolt/include/bolt/Core/BinaryContext.h:18,
                 from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/bolt/include/bolt/Core/BinaryFunction.h:29,
                 from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/bolt/lib/Target/X86/X86MCSymbolizer.h:12,
                 from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/bolt/lib/Target/X86/X86MCPlusBuilder.cpp:16:
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/bolt/include/bolt/Core/DebugData.h:512:22: warning: ‘maybe_unused’ attribute ignored [-Wattributes]
  512 |   DenseSet<uint64_t> DebugStrOffsetFinalized;
      |                      ^~~~~~~~~~~~~~~~~~~~~~~
11.574 [171/14/203] Building CXX object lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o
FAILED: lib/Transforms/Utils/CMakeFiles/LLVMTransformUtils.dir/SimplifyCFG.cpp.o 
ccache /usr/bin/c++ -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/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/build/lib/Transforms/Utils -I/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils -I/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/build/include -I/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-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 /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp: In function ‘bool sinkCommonCodeFromPredecessors(llvm::BasicBlock*, llvm::DomTreeUpdater*)’:
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2503:3: error: reference to ‘LockstepReverseIterator’ is ambiguous
 2503 |   LockstepReverseIterator<true> LRI(UnconditionalPreds);
      |   ^~~~~~~~~~~~~~~~~~~~~~~
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1787:7: note: candidates are: ‘class {anonymous}::LockstepReverseIterator’
 1787 | class LockstepReverseIterator {
      |       ^~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:77:
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/include/llvm/Transforms/Utils/LockstepReverseIterator.h:41:7: note:                 ‘template<bool EarlyFailure> class llvm::LockstepReverseIterator’
   41 | class LockstepReverseIterator
      |       ^~~~~~~~~~~~~~~~~~~~~~~
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2503:33: error: ‘LRI’ was not declared in this scope
 2503 |   LockstepReverseIterator<true> LRI(UnconditionalPreds);
      |                                 ^~~
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2533:44: error: reference to ‘LockstepReverseIterator’ is ambiguous
 2533 |     auto ProfitableToSinkInstruction = [&](LockstepReverseIterator<true> &LRI) {
      |                                            ^~~~~~~~~~~~~~~~~~~~~~~
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1787:7: note: candidates are: ‘class {anonymous}::LockstepReverseIterator’
 1787 | class LockstepReverseIterator {
      |       ^~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:77:
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/include/llvm/Transforms/Utils/LockstepReverseIterator.h:41:7: note:                 ‘template<bool EarlyFailure> class llvm::LockstepReverseIterator’
   41 | class LockstepReverseIterator
      |       ^~~~~~~~~~~~~~~~~~~~~~~
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2533:44: error: ‘LockstepReverseIterator’ has not been declared
 2533 |     auto ProfitableToSinkInstruction = [&](LockstepReverseIterator<true> &LRI) {
      |                                            ^~~~~~~~~~~~~~~~~~~~~~~
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2533:67: error: expected ‘,’ or ‘...’ before ‘<’ token
 2533 |     auto ProfitableToSinkInstruction = [&](LockstepReverseIterator<true> &LRI) {
      |                                                                   ^
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp: At global scope:
/home/worker/bolt-worker2/bolt-x86_64-ubuntu-nfc/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2206:13: warning: ‘bool canSinkInstructions(llvm::ArrayRef<llvm::Instruction*>, llvm::DenseMap<const llvm::Use*, llvm::SmallVector<llvm::Value*, 4> >&)’ defined but not used [-Wunused-function]
 2206 | static bool canSinkInstructions(
      |             ^~~~~~~~~~~~~~~~~~~
11.589 [171/13/204] Linking CXX static library lib/libLLVMBOLTUtils.a
11.780 [171/12/205] Building RISCVGenO0PreLegalizeGICombiner.inc...
12.155 [171/11/206] Building RISCVGenPostLegalizeGICombiner.inc...

```

</details>

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