[clang-tools-extra] [llvm] [llvm] add support for mustache templating language (PR #105893)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `polly-x86_64-linux` running on `polly-x86_64-gce1` while building `llvm` at step 5 "build".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/105/builds/7318

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

```
Step 5 (build) failure: 'ninja' (failure)
...
[344/4171] Copying clang's lsxintrin.h...
[345/4171] Copying clang's hlsl/hlsl_alias_intrinsics.h...
[346/4171] Copying clang's opencl-c-base.h...
[347/4171] Copying clang's avx512vlintrin.h...
[348/4171] Copying clang's htmxlintrin.h...
[349/4171] Copying clang's htmintrin.h...
[350/4171] Copying clang's opencl-c.h...
[351/4171] Copying clang's altivec.h...
[352/4171] Copying clang's riscv_bitmanip.h...
[353/4171] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Mustache.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/Mustache.cpp.o 
ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.obj/lib/Support -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.obj/include -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -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 -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -UNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/Mustache.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/Mustache.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/Mustache.cpp.o -c /home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp:109:12: error: declaration of ‘{anonymous}::Accessor llvm::mustache::Token::Accessor’ changes meaning of ‘Accessor’ [-fpermissive]
  109 |   Accessor Accessor;
      |            ^~~~~~~~
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp:19:7: note: ‘Accessor’ declared here as ‘using Accessor = class llvm::SmallVector<std::__cxx11::basic_string<char> >’
   19 | using Accessor = SmallVector<std::string>;
      |       ^~~~~~~~
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp:186:18: error: declaration of ‘const Accessor llvm::mustache::ASTNode::Accessor’ changes meaning of ‘Accessor’ [-fpermissive]
  186 |   const Accessor Accessor;
      |                  ^~~~~~~~
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp:19:7: note: ‘Accessor’ declared here as ‘using Accessor = class llvm::SmallVector<std::__cxx11::basic_string<char> >’
   19 | using Accessor = SmallVector<std::string>;
      |       ^~~~~~~~
In file included from /home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp:8:
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/include/llvm/Support/Mustache.h: In constructor ‘llvm::mustache::Template::Template(llvm::mustache::Template&&)’:
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/include/llvm/Support/Mustache.h:123:12: warning: ‘llvm::mustache::Template::Tree’ will be initialized after [-Wreorder]
  123 |   ASTNode *Tree;
      |            ^~~~
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/include/llvm/Support/Mustache.h:120:26: warning:   ‘llvm::BumpPtrAllocator llvm::mustache::Template::AstAllocator’ [-Wreorder]
  120 |   llvm::BumpPtrAllocator AstAllocator;
      |                          ^~~~~~~~~~~~
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/Support/Mustache.cpp:769:1: warning:   when initialized here [-Wreorder]
  769 | Template::Template(Template &&Other) noexcept
      | ^~~~~~~~
[354/4171] Copying clang's riscv_corev_alu.h...
[355/4171] Copying clang's riscv_crypto.h...
[356/4171] Copying clang's s390intrin.h...
[357/4171] Copying clang's sifive_vector.h...
[358/4171] Copying clang's riscv_ntlh.h...
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/105893