[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 `clang-cmake-x86_64-avx512-linux` running on `avx512-intel64` while building `llvm` at step 6 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/133/builds/10660

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

```
Step 6 (build stage 1) failure: 'ninja' (failure)
...
[18/124] Generating ../../bin/llvm-windres
[19/124] Linking CXX executable bin/llvm-tli-checker
[20/124] Linking CXX executable bin/llvm-debuginfod-find
[21/124] Linking CXX executable bin/yaml2obj
[22/124] Linking CXX executable bin/clang-format
[23/124] Linking CXX executable bin/llvm-ar
[24/124] Generating ../../bin/llvm-ranlib
[25/124] Generating ../../bin/llvm-lib
[26/124] Generating ../../bin/llvm-dlltool
[27/124] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o 
/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/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/lib/CodeGen -I/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/lib/CodeGen -I/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/include -I/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/include -march=cascadelake -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 -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -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 /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/lib/CodeGen/CFIFixup.cpp
/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/lib/CodeGen/CFIFixup.cpp: In function ‘llvm::SmallVector<BlockFlags> computeBlockInfo(const llvm::MachineFunction&, const llvm::MachineBasicBlock*)’:
/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/lib/CodeGen/CFIFixup.cpp:174:10: error: could not convert ‘BlockInfo’ from ‘SmallVector<[...],32>’ to ‘SmallVector<[...],40>’
  174 |   return BlockInfo;
      |          ^~~~~~~~~
      |          |
      |          SmallVector<[...],32>
[28/124] Linking CXX executable bin/llvm-debuginfod
[29/124] Linking CXX executable bin/llvm-readtapi
[30/124] Linking CXX executable bin/llvm-xray
[31/124] Linking CXX executable bin/llvm-symbolizer
[32/124] Linking CXX executable bin/llvm-cxxdump
[33/124] Linking CXX executable bin/obj2yaml
[34/124] Linking CXX executable bin/llvm-size
[35/124] Linking CXX executable bin/llvm-dwarfdump
[36/124] Linking CXX executable bin/llvm-cov
[37/124] Linking CXX executable bin/clang-offload-bundler
[38/124] Linking CXX executable bin/sancov
[39/124] Linking CXX executable bin/llvm-profdata
[40/124] Linking CXX executable bin/sanstats
[41/124] Linking CXX executable bin/llvm-ifs
[42/124] Linking CXX executable bin/llvm-cat
[43/124] Linking CXX executable bin/verify-uselistorder
[44/124] Linking CXX executable bin/llvm-objcopy
[45/124] Linking CXX executable bin/llvm-as
[46/124] Linking CXX executable bin/llvm-cfi-verify
[47/124] Linking CXX executable bin/llvm-modextract
[48/124] Linking CXX executable bin/llvm-rtdyld
[49/124] Linking CXX executable bin/llvm-debuginfo-analyzer
[50/124] Linking CXX executable bin/llvm-objdump
[51/124] Linking CXX executable bin/llvm-pdbutil
[52/124] Linking CXX executable bin/llvm-readobj
[53/124] Linking CXX executable bin/llvm-nm
[54/124] Linking CXX executable bin/llvm-link
[55/124] Linking CXX executable bin/llvm-profgen
[56/124] Linking CXX executable bin/diagtool
[57/124] Linking CXX shared module lib/CheckerDependencyHandlingAnalyzerPlugin.so
[58/124] Linking CXX executable bin/clang-diff

```

</details>

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