[llvm] [CFIFixup] Factor logic into helpers and use range-based loops (NFC) (PR #125137)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `cross-project-tests-sie-ubuntu-dwarf5` running on `doug-worker-1b` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/163/builds/12726

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
5.462 [103/8/18] Linking CXX executable bin/llvm-ar
5.479 [102/8/19] Generating ../../bin/llvm-dlltool
5.497 [101/8/20] Generating ../../bin/llvm-lib
5.514 [100/8/21] Generating ../../bin/llvm-ranlib
5.608 [99/8/22] Linking CXX executable bin/llvm-profdata
5.751 [98/8/23] Linking CXX executable bin/llvm-cat
5.883 [97/8/24] Linking CXX executable bin/llvm-as
5.886 [96/8/25] Linking CXX executable bin/sanstats
6.026 [95/8/26] Linking CXX executable bin/apinotes-test
6.566 [94/8/27] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o 
/opt/ccache/bin/g++ -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/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/lib/CodeGen -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/include -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/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/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o -MF lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o.d -o lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o -c /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen/CFIFixup.cpp
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen/CFIFixup.cpp: In function ‘llvm::SmallVector<BlockFlags> computeBlockInfo(const llvm::MachineFunction&, const llvm::MachineBasicBlock*)’:
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen/CFIFixup.cpp:174:10: error: could not convert ‘BlockInfo’ from ‘SmallVector<[...],32>’ to ‘SmallVector<[...],40>’
  174 |   return BlockInfo;
      |          ^~~~~~~~~
      |          |
      |          SmallVector<[...],32>
7.611 [94/7/28] Linking CXX shared module lib/SampleAnalyzerPlugin.so
7.674 [94/6/29] Linking CXX shared module lib/CheckerDependencyHandlingAnalyzerPlugin.so
7.800 [94/5/30] Linking CXX shared module lib/CheckerOptionHandlingAnalyzerPlugin.so
7.855 [94/4/31] Linking CXX executable bin/diagtool
8.555 [94/3/32] Linking CXX executable bin/clang-diff
20.494 [94/2/33] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/AsmPrinter.cpp.o
21.470 [94/1/34] Building CXX object lib/LTO/CMakeFiles/LLVMLTO.dir/LTO.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/125137