[clang] [clang][ssaf] Add accessor for `LUNamespace` (PR #195756)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-sparc64-linux` running on `debian-stadler-sparc64` while building `clang` at step 6 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/114/builds/574

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

```
Step 6 (build stage 1) failure: 'ninja' (failure)
...
[206/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/CodeViewRecordIO.cpp.o
[207/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/DebugChecksumsSubsection.cpp.o
[208/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/DebugFrameDataSubsection.cpp.o
[209/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/DebugSubsectionRecord.cpp.o
[210/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/DebugInlineeLinesSubsection.cpp.o
[211/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/DebugCrossImpSubsection.cpp.o
[212/4299] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/Line.cpp.o
[213/4299] Building CXX object utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/ARMTargetDefEmitter.cpp.o
[214/4299] Building CXX object lib/Bitstream/Reader/CMakeFiles/LLVMBitstreamReader.dir/BitstreamReader.cpp.o
[215/4299] Building CXX object lib/DebugInfo/MSF/CMakeFiles/LLVMDebugInfoMSF.dir/MSFBuilder.cpp.o
FAILED: [code=1] lib/DebugInfo/MSF/CMakeFiles/LLVMDebugInfoMSF.dir/MSFBuilder.cpp.o 
/usr/bin/c++ -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GLIBCXX_USE_CXX11_ABI=1 -D_GNU_SOURCE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/lib/DebugInfo/MSF -I/var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/lib/DebugInfo/MSF -I/var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/include -I/var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-dangling-reference -Wno-redundant-move -Wno-pessimizing-move -Wno-array-bounds -Wno-stringop-overread -Wno-dangling-pointer -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 -UNDEBUG -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/DebugInfo/MSF/CMakeFiles/LLVMDebugInfoMSF.dir/MSFBuilder.cpp.o -MF lib/DebugInfo/MSF/CMakeFiles/LLVMDebugInfoMSF.dir/MSFBuilder.cpp.o.d -o lib/DebugInfo/MSF/CMakeFiles/LLVMDebugInfoMSF.dir/MSFBuilder.cpp.o -c /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/lib/DebugInfo/MSF/MSFBuilder.cpp
In file included from /usr/include/c++/15/bits/shared_ptr_atomic.h:33,
                 from /usr/include/c++/15/memory:83,
                 from /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/include/llvm/ADT/STLExtras.h:36,
                 from /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/include/llvm/ADT/ArrayRef.h:13,
                 from /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/include/llvm/DebugInfo/MSF/MSFBuilder.h:12,
                 from /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/llvm/lib/DebugInfo/MSF/MSFBuilder.cpp:9:
/usr/include/c++/15/bits/atomic_base.h:682:12: error: specialization of ‘template<class _IntTp> struct std::__atomic_base’ must appear at namespace scope [-Wtemplate-body]
  682 |     struct __atomic_base<_PTp*>
      |            ^~~~~~~~~~~~~~~~~~~~
/usr/include/c++/15/bits/atomic_base.h:949:3: error: expected unqualified-id before ‘namespace’ [-Wtemplate-body]
  949 |   namespace __atomic_impl
      |   ^~~~~~~~~
/usr/include/c++/15/bits/atomic_base.h:2109:2: error: expected ‘;’ after struct definition
 2109 | } // namespace std
      |  ^
      |  ;
In member function ‘std::__atomic_base<_IntTp>::operator __int_type() const’:
cc1plus: error: duplicate ‘static’ specifier [-Wtemplate-body]
/usr/include/c++/15/bits/atomic_base.h:363:44: error: expected unqualified-id before ‘noexcept’ [-Wtemplate-body]
  363 |       operator __int_type() const volatile noexcept
      |                                            ^~~~~~~~
/usr/include/c++/15/bits/atomic_base.h:368:7: error: a function-definition is not allowed here before ‘{’ token [-Wtemplate-body]
  368 |       {
      |       ^
/usr/include/c++/15/bits/atomic_base.h:375:7: error: a function-definition is not allowed here before ‘{’ token [-Wtemplate-body]
  375 |       {
      |       ^
/usr/include/c++/15/bits/atomic_base.h:382:7: error: a function-definition is not allowed here before ‘{’ token [-Wtemplate-body]
  382 |       { return fetch_add(1); }
      |       ^
/usr/include/c++/15/bits/atomic_base.h:386:7: error: a function-definition is not allowed here before ‘{’ token [-Wtemplate-body]
  386 |       { return fetch_add(1); }
      |       ^
/usr/include/c++/15/bits/atomic_base.h:390:7: error: a function-definition is not allowed here before ‘{’ token [-Wtemplate-body]
  390 |       { return fetch_sub(1); }
      |       ^
/usr/include/c++/15/bits/atomic_base.h:394:7: error: a function-definition is not allowed here before ‘{’ token [-Wtemplate-body]

```

</details>

https://github.com/llvm/llvm-project/pull/195756