[clang-tools-extra] [clang-doc] Add helpers for Template config (PR #138062)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-multistage` running on `ppc64le-clang-multistage-test` while building `clang-tools-extra` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/76/builds/9814

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
...
[77/85] Generating POWERPC64LELinuxConfig/Asan-powerpc64le-inline-Noinst-Test
[78/85] Generating ASAN_NOINST_TEST_OBJECTS.gtest-all.cc.powerpc64le-calls.o
[79/85] Generating POWERPC64LELinuxConfig/Asan-powerpc64le-calls-Noinst-Test
[80/85] Generating ASAN_INST_TEST_OBJECTS.gtest-all.cc.powerpc64le-calls.o
[81/85] Generating POWERPC64LELinuxDynamicConfig/Asan-powerpc64le-calls-Dynamic-Test
[82/85] Generating POWERPC64LELinuxConfig/Asan-powerpc64le-calls-Test
[83/85] Generating ASAN_INST_TEST_OBJECTS.gtest-all.cc.powerpc64le-inline.o
[84/85] Generating POWERPC64LELinuxDynamicConfig/Asan-powerpc64le-inline-Dynamic-Test
[85/85] Generating POWERPC64LELinuxConfig/Asan-powerpc64le-inline-Test
[1209/1214] Linking CXX executable tools/clang/tools/extra/unittests/clang-doc/ClangDocTests
FAILED: tools/clang/tools/extra/unittests/clang-doc/ClangDocTests 
: && /usr/lib64/ccache/c++ -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-noexcept-type -Wno-unnecessary-virtual-specifier -Wdelete-non-virtual-dtor -Wno-comment -Wno-misleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -fno-strict-aliasing -O3 -DNDEBUG -Wl,--gc-sections tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/BitcodeTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/ClangDocTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/GeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/HTMLGeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/HTMLMustacheGeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/MDGeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/MergeTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/SerializeTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/YAMLGeneratorTest.cpp.o -o tools/clang/tools/extra/unittests/clang-doc/ClangDocTests  -Wl,-rpath,/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1/lib  -lpthread  lib/libllvm_gtest_main.so.21.0git  -lpthread  lib/libclangDoc.so.21.0git  lib/libLLVMTestingSupport.so.21.0git  lib/libclangTooling.so.21.0git  lib/libclangFormat.so.21.0git  lib/libclangFrontend.so.21.0git  lib/libclangSerialization.so.21.0git  lib/libclangToolingCore.so.21.0git  lib/libclangRewrite.so.21.0git  lib/libclangASTMatchers.so.21.0git  lib/libclangAST.so.21.0git  lib/libclangBasic.so.21.0git  lib/libLLVMFrontendOpenMP.so.21.0git  lib/libLLVMBitstreamReader.so.21.0git  lib/libllvm_gtest.so.21.0git  lib/libLLVMSupport.so.21.0git  -Wl,-rpath-link,/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1/lib && :
/usr/bin/ld: tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/HTMLMustacheGeneratorTest.cpp.o: undefined reference to symbol '_Z20getMustacheHtmlFilesN4llvm9StringRefERN5clang3doc15ClangDocContextE'
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1/lib/libclangDocSupport.so.21.0git: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
Step 11 (ninja check 2) failure: stage 2 checked (failure)
...
2 warning(s) in tests

Testing Time: 179.69s

Total Discovered Tests: 4404
  Skipped          :    9 (0.20%)
  Unsupported      : 1184 (26.88%)
  Passed           : 3169 (71.96%)
  Expectedly Failed:   42 (0.95%)
[1148/1214] Linking CXX executable tools/clang/tools/extra/unittests/clang-doc/ClangDocTests
FAILED: tools/clang/tools/extra/unittests/clang-doc/ClangDocTests 
: && /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1.install/bin/clang++ -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wno-unnecessary-virtual-specifier -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -Wno-nested-anon-types -O3 -DNDEBUG -Wl,--gc-sections tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/BitcodeTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/ClangDocTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/GeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/HTMLGeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/HTMLMustacheGeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/MDGeneratorTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/MergeTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/SerializeTest.cpp.o tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/YAMLGeneratorTest.cpp.o -o tools/clang/tools/extra/unittests/clang-doc/ClangDocTests  -Wl,-rpath,/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/lib  -lpthread  lib/libllvm_gtest_main.so.21.0git  -lpthread  lib/libclangDoc.so.21.0git  lib/libLLVMTestingSupport.so.21.0git  lib/libclangTooling.so.21.0git  lib/libclangFormat.so.21.0git  lib/libclangFrontend.so.21.0git  lib/libclangSerialization.so.21.0git  lib/libclangToolingCore.so.21.0git  lib/libclangRewrite.so.21.0git  lib/libclangASTMatchers.so.21.0git  lib/libclangAST.so.21.0git  lib/libclangBasic.so.21.0git  lib/libLLVMFrontendOpenMP.so.21.0git  lib/libLLVMBitstreamReader.so.21.0git  lib/libllvm_gtest.so.21.0git  lib/libLLVMSupport.so.21.0git  -Wl,-rpath-link,/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/lib && :
/usr/bin/ld: tools/clang/tools/extra/unittests/clang-doc/CMakeFiles/ClangDocTests.dir/HTMLMustacheGeneratorTest.cpp.o: undefined reference to symbol '_Z20getMustacheHtmlFilesN4llvm9StringRefERN5clang3doc15ClangDocContextE'
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/lib/libclangDocSupport.so.21.0git: error adding symbols: DSO missing from command line
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
[1205/1214] Building CXX object tools/clang/tools/extra/clangd/unittests/CMakeFiles/ClangdTests.dir/CodeCompleteTests.cpp.o
[1207/1214] Building CXX object tools/clang/unittests/CMakeFiles/AllClangUnitTests.dir/ASTMatchers/ASTMatchersTraversalTest.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/138062