[llvm] [LoopInfo] Avoid a throwaway vector in getLoopsInPreorder. NFC (PR #207607)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-aarch64-windows` running on `linaro-armv8-windows-msvc-05` while building `llvm` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/141/builds/20272

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

```
Step 6 (test) failure: build (failure)
...
UNSUPPORTED: lldb-api :: lang/c/blocks/TestBlocks.py (806 of 2611)
PASS: lldb-api :: lang/c/builtin-types/TestCBuiltinTypes.py (807 of 2611)
PASS: lldb-api :: lang/c/anonymous/TestAnonymous.py (808 of 2611)
UNSUPPORTED: lldb-api :: lang/c/complex/TestComplexC99.py (809 of 2611)
UNSUPPORTED: lldb-api :: lang/c/complex_int/TestComplexInt.py (810 of 2611)
XFAIL: lldb-api :: lang/c/conflicting-symbol/TestConflictingSymbol.py (811 of 2611)
PASS: lldb-api :: lang/c/calling-conventions/TestCCallingConventions.py (812 of 2611)
UNSUPPORTED: lldb-api :: lang/c/cpp_keyword_identifiers/TestCppKeywordsAsCIdentifiers.py (813 of 2611)
XFAIL: lldb-api :: lang/c/const_variables/TestConstVariables.py (814 of 2611)
PASS: lldb-api :: lang/c/find_struct_type/TestFindStructTypes.py (815 of 2611)
FAIL: lldb-api :: lang/c/enum_types/TestEnumTypes.py (816 of 2611)
******************** TEST 'lldb-api :: lang/c/enum_types/TestEnumTypes.py' FAILED ********************
Script:
--
C:/Users/tcwg/scoop/apps/python/current/python.exe C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/llvm-project/lldb\test\API\dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./lib --env LLVM_INCLUDE_DIR=C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/include --env LLVM_TOOLS_DIR=C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin --triple aarch64-pc-windows-msvc --build-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build --lldb-module-cache-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build/module-cache-lldb\lldb-api --clang-module-cache-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build/module-cache-clang\lldb-api --executable C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/lldb.exe --lldb-python-dir C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\Lib\site-packages --compiler C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/clang.exe --dsymutil C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/dsymutil.exe --make C:/Users/tcwg/scoop/shims/make.exe --llvm-tools-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin --lldb-obj-root C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/tools/lldb --lldb-libs-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./lib --cmake-build-type Release --skip-category=watchpoint --env LLDB_LAUNCH_FLAG_USE_PIPES=1 C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\test\API\lang\c\enum_types -p TestEnumTypes.py
--
Exit Code: 1

Command Output (stdout):
--
Skipping the following test categories: watchpoint, libc++, libstdcxx, dwo, dsym, gmodules, debugserver, objc, fork, pexpect


--
Command Output (stderr):
--
UNSUPPORTED: LLDB (C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe-aarch64) :: test_api_dsym (TestEnumTypes.EnumTypesTestCase.test_api_dsym) (test case does not fall in any category of interest for this run) 

PASS: LLDB (C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe-aarch64) :: test_api_dwarf (TestEnumTypes.EnumTypesTestCase.test_api_dwarf)

UNSUPPORTED: LLDB (C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe-aarch64) :: test_api_dwo (TestEnumTypes.EnumTypesTestCase.test_api_dwo) (test case does not fall in any category of interest for this run) 

UNSUPPORTED: LLDB (C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe-aarch64) :: test_command_line_dsym (TestEnumTypes.EnumTypesTestCase.test_command_line_dsym) (test case does not fall in any category of interest for this run) 

FAIL: LLDB (C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe-aarch64) :: test_command_line_dwarf (TestEnumTypes.EnumTypesTestCase.test_command_line_dwarf)

Log Files:

 - C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\lldb-test-build\lang\c\enum_types\TestEnumTypes\Failure_test_command_line_dwarf.log

UNSUPPORTED: LLDB (C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe-aarch64) :: test_command_line_dwo (TestEnumTypes.EnumTypesTestCase.test_command_line_dwo) (test case does not fall in any category of interest for this run) 

======================================================================

FAIL: test_command_line_dwarf (TestEnumTypes.EnumTypesTestCase.test_command_line_dwarf)

   Test 'image lookup -t enum_test_days' and check for correct display and enum value printing.

----------------------------------------------------------------------

```

</details>

https://github.com/llvm/llvm-project/pull/207607