Clang-CL compiler error : cannot mangle this 'auto' type yet

Question

Clang-CL compiler error : cannot mangle this 'auto' type yet

Context :

• Clang-CL compilation attempts currently results in the following error in several of my codebases :

cannot mangle this 'auto' type yet

Because this error message does not come with a filename nor an error line,
it is pretty hard to locate what code is its root cause.

In addition, and for information purpose, here is a complete log for instance :

[1/2] Building CXX object tests\CMakeFiles\gcl_test_binary.dir\Main.cpp.obj
FAILED: tests/CMakeFiles/gcl_test_binary.dir/Main.cpp.obj 
  C:\PROGRA~2\MICROS~1\2019\COMMUN~1\VC\Tools\Llvm\x64\bin\clang-cl.exe  /nologo -TP  -I..\..\..\includes -m64 -fdiagnostics-absolute-paths  /DWIN32 /D_WINDOWS /W3 /GR /EHsc /MDd /Zi /Ob0 /Od /RTC1 -std:c++latest /showIncludes /Fotests\CMakeFiles\gcl_test_binary.dir\Main.cpp.obj /Fdtests\CMakeFiles\gcl_test_binary.dir\ -c -- ..\..\..\tests\Main.cpp
gcl_cpp\out\build\x64-Clang-Debug\EXEC : error : cannot mangle this 'auto' type yet

1 error generated.
  ninja: build stopped: subcommand failed.

Question : Does anyone knows a convenient trick to identity where does that error comes from ?

Hint : I suspect this part of the compiler sources (see here on github):

void MicrosoftCXXNameMangler::mangleType(const AutoType *T, Qualifiers,
                                         SourceRange Range) {
  assert(T->getDeducedType().isNull() && "expecting a dependent type!");

  DiagnosticsEngine &Diags = Context.getDiags();
  unsigned DiagID = Diags.getCustomDiagID(DiagnosticsEngine::Error,
    "cannot mangle this 'auto' type yet");
  Diags.Report(Range.getBegin(), DiagID)
    << Range;
}