[clang] [ClangScanDeps] Avoid use-of-uninitialized-memory for end-of-directive edge case (PR #188590)

[LLVM Continuous Integration via cfe-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 `clang` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/141/builds/16698

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

```
Step 6 (test) failure: build (failure)
...
UNSUPPORTED: lldb-api :: iohandler/unicode/TestUnicode.py (768 of 2485)
UNSUPPORTED: lldb-api :: lang/BoundsSafety/soft_trap/TestBoundsSafetyInstrumentationPlugin.py (769 of 2485)
PASS: lldb-api :: lang/c/anonymous/TestAnonymous.py (770 of 2485)
PASS: lldb-api :: lang/c/array_types/TestArrayTypes.py (771 of 2485)
UNSUPPORTED: lldb-api :: lang/c/bitfields/TestBitfields.py (772 of 2485)
UNSUPPORTED: lldb-api :: lang/c/blocks/TestBlocks.py (773 of 2485)
PASS: lldb-api :: lang/c/builtin-types/TestCBuiltinTypes.py (774 of 2485)
PASS: lldb-api :: lang/c/calling-conventions/TestCCallingConventions.py (775 of 2485)
UNSUPPORTED: lldb-api :: lang/c/complex/TestComplexC99.py (776 of 2485)
TIMEOUT: lldb-api :: functionalities/breakpoint/two_hits_one_actual/TestTwoHitsOneActual.py (777 of 2485)
******************** TEST 'lldb-api :: functionalities/breakpoint/two_hits_one_actual/TestTwoHitsOneActual.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 --arch aarch64 --build-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build.noindex --lldb-module-cache-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build.noindex/module-cache-lldb\lldb-api --clang-module-cache-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build.noindex/module-cache-clang\lldb-api --executable C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/lldb.exe --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 C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\test\API\functionalities\breakpoint\two_hits_one_actual -p TestTwoHitsOneActual.py
--
Exit Code: 15
Timeout: Reached timeout of 600 seconds

Command Output (stdout):
--
lldb version 23.0.0git (https://github.com/llvm/llvm-project.git revision f1889a73e63d3183657452c75fbde8b98e378b7c)
  clang revision f1889a73e63d3183657452c75fbde8b98e378b7c
  llvm revision f1889a73e63d3183657452c75fbde8b98e378b7c

--

********************
UNSUPPORTED: lldb-api :: lang/c/complex_int/TestComplexInt.py (778 of 2485)
XFAIL: lldb-api :: lang/c/const_variables/TestConstVariables.py (779 of 2485)
XFAIL: lldb-api :: lang/c/conflicting-symbol/TestConflictingSymbol.py (780 of 2485)
UNSUPPORTED: lldb-api :: lang/c/cpp_keyword_identifiers/TestCppKeywordsAsCIdentifiers.py (781 of 2485)
PASS: lldb-api :: lang/c/find_struct_type/TestFindStructTypes.py (782 of 2485)
PASS: lldb-api :: lang/c/enum_types/TestEnumTypes.py (783 of 2485)
PASS: lldb-api :: lang/c/flexible-array-members/TestCFlexibleArrayMembers.py (784 of 2485)
PASS: lldb-api :: lang/c/forward/TestForwardDeclaration.py (785 of 2485)
PASS: lldb-api :: lang/c/fpeval/TestFPEval.py (786 of 2485)
UNSUPPORTED: lldb-api :: lang/c/full_lto_stepping/TestFullLtoStepping.py (787 of 2485)
PASS: lldb-api :: lang/c/function_types/TestFunctionTypes.py (788 of 2485)
XFAIL: lldb-api :: lang/c/global_variables/TestGlobalVariables.py (789 of 2485)
XFAIL: lldb-api :: lang/c/local_types/TestUseClosestType.py (790 of 2485)
PASS: lldb-api :: lang/c/inlines/TestRedefinitionsInInlines.py (791 of 2485)
PASS: lldb-api :: lang/c/local_variables/TestLocalVariables.py (792 of 2485)
XFAIL: lldb-api :: lang/c/modules/TestCModules.py (793 of 2485)
PASS: lldb-api :: lang/c/non-mangled/TestCNonMangled.py (794 of 2485)
PASS: lldb-api :: lang/c/offsetof/TestOffsetof.py (795 of 2485)
UNSUPPORTED: lldb-api :: lang/c/ptrauth/TestPtrAuth.py (796 of 2485)
PASS: lldb-api :: lang/c/parray_vrs_char_array/TestParrayVrsCharArrayChild.py (797 of 2485)
PASS: lldb-api :: lang/c/record_decl_in_expr/TestRecordDeclInExpr.py (798 of 2485)
PASS: lldb-api :: lang/c/register_variables/TestRegisterVariables.py (799 of 2485)

```

</details>

https://github.com/llvm/llvm-project/pull/188590