[llvm] [llvm][support] Add LDBG macro. (PR #143704)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu-no-asserts` running on `doug-worker-6` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/202/builds/2474

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
-- Performing Test COMPILER_RT_TARGET_HAS_UNAME - Success
-- Performing Test HAS_THREAD_LOCAL
-- Performing Test HAS_THREAD_LOCAL - Success
-- Generated Sanitizer SUPPORTED_TOOLS list on "Linux" is "asan;lsan;hwasan;msan;tsan;ubsan"
-- sanitizer_common tests on "Linux" will run against "asan;lsan;hwasan;msan;tsan;ubsan"
-- check-shadowcallstack does nothing.
-- Configuring done
-- Generating done
-- Build files have been written to: /home/buildbot/buildbot-root/gcc-no-asserts/build/runtimes/runtimes-bins
317.781 [155/8/7115] Building CXX object unittests/Support/CMakeFiles/SupportTests.dir/DebugLogTest.cpp.o
FAILED: unittests/Support/CMakeFiles/SupportTests.dir/DebugLogTest.cpp.o 
/opt/ccache/bin/g++ -DEXPERIMENTAL_KEY_INSTRUCTIONS -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_STATIC -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/buildbot/buildbot-root/gcc-no-asserts/build/unittests/Support -I/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/unittests/Support -I/home/buildbot/buildbot-root/gcc-no-asserts/build/include -I/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/include -I/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/third-party/unittest/googletest/include -I/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/third-party/unittest/googlemock/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-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 -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -Wno-dangling-else -Wno-variadic-macros -fno-exceptions -funwind-tables -fno-rtti -Wno-suggest-override -std=c++17 -MD -MT unittests/Support/CMakeFiles/SupportTests.dir/DebugLogTest.cpp.o -MF unittests/Support/CMakeFiles/SupportTests.dir/DebugLogTest.cpp.o.d -o unittests/Support/CMakeFiles/SupportTests.dir/DebugLogTest.cpp.o -c /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/unittests/Support/DebugLogTest.cpp
/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/unittests/Support/DebugLogTest.cpp: In member function ‘virtual void DebugLogTest_Basic_Test::TestBody()’:
/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/unittests/Support/DebugLogTest.cpp:69:22: error: zero-size array ‘DT’
   69 |   static const char *DT[] = {};
      |                      ^~
319.101 [155/2/7121] Linking CXX executable unittests/Target/TargetMachineCTests
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/143704