[clang] [clang] Serialization: support hashing null template arguments (PR #141890)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-x86_64-debian` running on `lldb-x86_64-debian` while building `clang` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/23407

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

```
Step 6 (test) failure: build (failure)
...
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Lua/io.test (2954 of 2965)
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Python/Crashlog/app_specific_backtrace_crashlog.test (2955 of 2965)
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Python/Crashlog/no-args.test (2956 of 2965)
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Python/Crashlog/altered_threadState.test (2957 of 2965)
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Lua/persistent_state.test (2958 of 2965)
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Python/Crashlog/parser_text.test (2959 of 2965)
UNSUPPORTED: lldb-shell :: Register/x86-gp-read.test (2960 of 2965)
UNSUPPORTED: lldb-shell :: ScriptInterpreter/Lua/bindings.test (2961 of 2965)
PASS: lldb-api :: terminal/TestEditlineCompletions.py (2962 of 2965)
UNRESOLVED: lldb-api :: tools/lldb-dap/launch/TestDAP_launch.py (2963 of 2965)
******************** TEST 'lldb-api :: tools/lldb-dap/launch/TestDAP_launch.py' FAILED ********************
Script:
--
/usr/bin/python3 /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./lib --env LLVM_INCLUDE_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/include --env LLVM_TOOLS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./bin --arch x86_64 --build-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex --lldb-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-lldb/lldb-api --clang-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-clang/lldb-api --executable /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/lldb --compiler /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/clang --dsymutil /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./bin --lldb-obj-root /home/worker/2.0.1/lldb-x86_64-debian/build/tools/lldb --lldb-libs-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./lib --cmake-build-type Release -t /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/tools/lldb-dap/launch -p TestDAP_launch.py
--
Exit Code: 1

Command Output (stdout):
--
lldb version 21.0.0git (https://github.com/llvm/llvm-project.git revision 61314076f78327ffd5e1463c35373c7f4e52d30f)
  clang revision 61314076f78327ffd5e1463c35373c7f4e52d30f
  llvm revision 61314076f78327ffd5e1463c35373c7f4e52d30f
Skipping the following test categories: ['libc++', 'dsym', 'gmodules', 'debugserver', 'objc']

--
Command Output (stderr):
--
Change dir to: /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/tools/lldb-dap/launch
runCmd: settings clear --all

output: 

runCmd: settings set symbols.enable-external-lookup false

output: 

runCmd: settings set target.inherit-tcc true

output: 

runCmd: settings set target.disable-aslr false

output: 

runCmd: settings set target.detach-on-error false

output: 

runCmd: settings set target.auto-apply-fixits false

```

</details>

https://github.com/llvm/llvm-project/pull/141890